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 $121.81   4.394%   $127.1623   $127.16   $127.15   $127.20  
  Purchase #2 $225.37   9.444%   $246.6539   $246.65   $246.65   $246.70  
  Purchase #3 $227.68   4.268%   $237.3974   $237.40   $237.40   $237.40  
  Purchase #4 $207.63   5.719%   $219.5044   $219.50   $219.50   $219.50  
  Purchase #5 $193.63   5.473%   $204.2274   $204.23   $204.25   $204.20  
  Purchase #6 $61.51   11.325%   $68.476   $68.48   $68.50   $68.50  
  Purchase #7 $86.53   4.170%   $90.1383   $90.14   $90.15   $90.10  
  7 purchase totals = $1,124.16       $1,193.5597   $1,193.56   $1,193.60   $1,193.60