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 $183.27   10.591%   $202.6801   $202.68   $202.70   $202.70  
  Purchase #2 $56.78   3.471%   $58.7508   $58.75   $58.75   $58.80  
  Purchase #3 $107.94   11.527%   $120.3822   $120.38   $120.40   $120.40  
  Purchase #4 $235.60   4.684%   $246.6355   $246.64   $246.65   $246.60  
  Purchase #5 $27.65   9.399%   $30.2488   $30.25   $30.25   $30.20  
  Purchase #6 $58.87   11.476%   $65.6259   $65.63   $65.65   $65.60  
  Purchase #7 $112.30   3.605%   $116.3484   $116.35   $116.35   $116.30  
  7 purchase totals = $782.41       $840.6717   $840.68   $840.75   $840.60