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 $111.30   7.488%   $119.6341   $119.63   $119.65   $119.60  
  Purchase #2 $160.95   11.557%   $179.551   $179.55   $179.55   $179.60  
  Purchase #3 $206.28   7.609%   $221.9758   $221.98   $222.00   $222.00  
  Purchase #4 $250.47   4.573%   $261.924   $261.92   $261.90   $261.90  
  Purchase #5 $202.73   13.591%   $230.283   $230.28   $230.30   $230.30  
  Purchase #6 $213.96   5.429%   $225.5759   $225.58   $225.60   $225.60  
  Purchase #7 $8.48   3.529%   $8.7793   $8.78   $8.80   $8.80  
  7 purchase totals = $1,154.17       $1,247.7231   $1,247.72   $1,247.80   $1,247.80