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 $74.65   13.276%   $84.5605   $84.56   $84.55   $84.60  
  Purchase #2 $207.84   6.608%   $221.5741   $221.57   $221.55   $221.60  
  Purchase #3 $41.86   3.685%   $43.4025   $43.40   $43.40   $43.40  
  Purchase #4 $68.45   11.584%   $76.3792   $76.38   $76.40   $76.40  
  Purchase #5 $54.39   12.403%   $61.136   $61.14   $61.15   $61.10  
  Purchase #6 $132.59   8.305%   $143.6016   $143.60   $143.60   $143.60  
  Purchase #7 $89.78   6.410%   $95.5349   $95.53   $95.55   $95.50  
  7 purchase totals = $669.56       $726.1888   $726.18   $726.20   $726.20