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 $44.41   11.733%   $49.6206   $49.62   $49.60   $49.60  
  Purchase #2 $208.82   7.147%   $223.7444   $223.74   $223.75   $223.70  
  Purchase #3 $132.29   12.624%   $148.9903   $148.99   $149.00   $149.00  
  Purchase #4 $82.38   9.582%   $90.2737   $90.27   $90.25   $90.30  
  Purchase #5 $150.53   11.375%   $167.6528   $167.65   $167.65   $167.70  
  Purchase #6 $64.77   10.427%   $71.5236   $71.52   $71.50   $71.50  
  Purchase #7 $65.36   7.145%   $70.03   $70.03   $70.05   $70.00  
  7 purchase totals = $748.56       $821.8354   $821.82   $821.80   $821.80