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 $110.80   4.322%   $115.5888   $115.59   $115.60   $115.60  
  Purchase #2 $123.83   9.544%   $135.6483   $135.65   $135.65   $135.60  
  Purchase #3 $177.46   8.783%   $193.0463   $193.05   $193.05   $193.00  
  Purchase #4 $63.38   5.579%   $66.916   $66.92   $66.90   $66.90  
  Purchase #5 $59.74   13.811%   $67.9907   $67.99   $68.00   $68.00  
  Purchase #6 $249.40   13.496%   $283.059   $283.06   $283.05   $283.10  
  Purchase #7 $124.95   5.167%   $131.4062   $131.41   $131.40   $131.40  
  7 purchase totals = $909.56       $993.6553   $993.67   $993.65   $993.60