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 $167.83   12.452%   $188.7282   $188.73   $188.75   $188.70  
  Purchase #2 $125.31   13.314%   $141.9938   $141.99   $142.00   $142.00  
  Purchase #3 $129.45   6.752%   $138.1905   $138.19   $138.20   $138.20  
  Purchase #4 $201.57   5.861%   $213.384   $213.38   $213.40   $213.40  
  Purchase #5 $161.94   8.434%   $175.598   $175.60   $175.60   $175.60  
  Purchase #6 $134.43   10.771%   $148.9095   $148.91   $148.90   $148.90  
  Purchase #7 $45.53   5.821%   $48.1803   $48.18   $48.20   $48.20  
  7 purchase totals = $966.06       $1,054.9843   $1,054.98   $1,055.05   $1,055.00