Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $117.98   6.425%   $125.5602   $125.56   $125.55   $125.60  
  Purchase #2 $246.72   10.337%   $272.2234   $272.22   $272.20   $272.20  
  Purchase #3 $231.48   6.276%   $246.0077   $246.01   $246.00   $246.00  
  Purchase #4 $236.60   4.758%   $247.8574   $247.86   $247.85   $247.90  
  Purchase #5 $120.63   3.699%   $125.0921   $125.09   $125.10   $125.10  
  Purchase #6 $127.26   10.337%   $140.4149   $140.41   $140.40   $140.40  
  Purchase #7 $106.58   11.645%   $118.9912   $118.99   $119.00   $119.00  
  7 purchase totals = $1,187.25       $1,276.1469   $1,276.14   $1,276.10   $1,276.20