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 $168.38   6.485%   $179.2994   $179.30   $179.30   $179.30  
  Purchase #2 $112.71   3.820%   $117.0155   $117.02   $117.00   $117.00  
  Purchase #3 $10.82   7.837%   $11.668   $11.67   $11.65   $11.70  
  Purchase #4 $43.82   5.149%   $46.0763   $46.08   $46.10   $46.10  
  Purchase #5 $242.60   13.762%   $275.9866   $275.99   $276.00   $276.00  
  Purchase #6 $102.91   4.567%   $107.6099   $107.61   $107.60   $107.60  
  Purchase #7 $84.31   10.622%   $93.2654   $93.27   $93.25   $93.30  
  7 purchase totals = $765.55       $830.9211   $830.94   $830.90   $831.00