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 $227.34   11.822%   $254.2161   $254.22   $254.20   $254.20  
  Purchase #2 $192.70   4.113%   $200.6258   $200.63   $200.65   $200.60  
  Purchase #3 $18.58   10.570%   $20.5439   $20.54   $20.55   $20.50  
  Purchase #4 $179.92   4.362%   $187.7681   $187.77   $187.75   $187.80  
  Purchase #5 $112.27   4.805%   $117.6646   $117.66   $117.65   $117.70  
  Purchase #6 $85.83   9.358%   $93.862   $93.86   $93.85   $93.90  
  Purchase #7 $237.76   11.768%   $265.7396   $265.74   $265.75   $265.70  
  7 purchase totals = $1,054.40       $1,140.4201   $1,140.42   $1,140.40   $1,140.40