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 $212.89   9.102%   $232.2672   $232.27   $232.25   $232.30  
  Purchase #2 $32.31   8.202%   $34.9601   $34.96   $34.95   $35.00  
  Purchase #3 $78.33   5.486%   $82.6272   $82.63   $82.65   $82.60  
  Purchase #4 $112.53   10.591%   $124.4481   $124.45   $124.45   $124.40  
  Purchase #5 $227.74   3.135%   $234.8796   $234.88   $234.90   $234.90  
  Purchase #6 $169.31   5.343%   $178.3562   $178.36   $178.35   $178.40  
  Purchase #7 $47.95   11.107%   $53.2758   $53.28   $53.30   $53.30  
  7 purchase totals = $881.06       $940.8142   $940.83   $940.85   $940.90