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 $66.79   12.433%   $75.094   $75.09   $75.10   $75.10  
  Purchase #2 $115.69   8.122%   $125.0863   $125.09   $125.10   $125.10  
  Purchase #3 $170.27   7.707%   $183.3927   $183.39   $183.40   $183.40  
  Purchase #4 $44.98   11.770%   $50.2741   $50.27   $50.25   $50.30  
  Purchase #5 $215.97   7.609%   $232.4032   $232.40   $232.40   $232.40  
  Purchase #6 $246.40   6.863%   $263.3104   $263.31   $263.30   $263.30  
  Purchase #7 $216.73   8.657%   $235.4923   $235.49   $235.50   $235.50  
  7 purchase totals = $1,076.83       $1,165.0530   $1,165.04   $1,165.05   $1,165.10