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 $62.94   4.819%   $65.9731   $65.97   $65.95   $66.00  
  Purchase #2 $43.76   6.417%   $46.5681   $46.57   $46.55   $46.60  
  Purchase #3 $67.77   11.232%   $75.3819   $75.38   $75.40   $75.40  
  Purchase #4 $167.61   7.104%   $179.517   $179.52   $179.50   $179.50  
  Purchase #5 $228.28   5.598%   $241.0591   $241.06   $241.05   $241.10  
  Purchase #6 $54.40   9.645%   $59.6469   $59.65   $59.65   $59.60  
  Purchase #7 $234.26   13.522%   $265.9366   $265.94   $265.95   $265.90  
  7 purchase totals = $859.02       $934.0827   $934.09   $934.05   $934.10