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 $107.65   7.399%   $115.615   $115.62   $115.60   $115.60  
  Purchase #2 $118.47   4.339%   $123.6104   $123.61   $123.60   $123.60  
  Purchase #3 $65.83   12.428%   $74.0114   $74.01   $74.00   $74.00  
  Purchase #4 $45.52   5.527%   $48.0359   $48.04   $48.05   $48.00  
  Purchase #5 $236.79   12.131%   $265.515   $265.52   $265.50   $265.50  
  Purchase #6 $126.94   8.259%   $137.424   $137.42   $137.40   $137.40  
  Purchase #7 $151.41   5.526%   $159.7769   $159.78   $159.80   $159.80  
  7 purchase totals = $852.61       $923.9886   $924.00   $923.95   $923.90