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 $98.27   5.837%   $104.006   $104.01   $104.00   $104.00  
  Purchase #2 $55.60   13.528%   $63.1216   $63.12   $63.10   $63.10  
  Purchase #3 $117.79   4.299%   $122.8538   $122.85   $122.85   $122.90  
  Purchase #4 $54.38   8.389%   $58.9419   $58.94   $58.95   $58.90  
  Purchase #5 $11.41   10.650%   $12.6252   $12.63   $12.65   $12.60  
  Purchase #6 $153.60   9.200%   $167.7312   $167.73   $167.75   $167.70  
  Purchase #7 $209.60   12.245%   $235.2655   $235.27   $235.25   $235.30  
  7 purchase totals = $700.65       $764.5452   $764.55   $764.55   $764.50