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 $67.28   12.127%   $75.439   $75.44   $75.45   $75.40  
  Purchase #2 $200.58   4.578%   $209.7626   $209.76   $209.75   $209.80  
  Purchase #3 $232.90   11.266%   $259.1385   $259.14   $259.15   $259.10  
  Purchase #4 $102.36   8.227%   $110.7812   $110.78   $110.80   $110.80  
  Purchase #5 $179.31   6.837%   $191.5694   $191.57   $191.55   $191.60  
  Purchase #6 $232.31   11.529%   $259.093   $259.09   $259.10   $259.10  
  Purchase #7 $143.86   11.348%   $160.1852   $160.19   $160.20   $160.20  
  7 purchase totals = $1,158.60       $1,265.9689   $1,265.97   $1,266.00   $1,266.00