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 $52.59   12.531%   $59.1801   $59.18   $59.20   $59.20  
  Purchase #2 $73.33   9.412%   $80.2318   $80.23   $80.25   $80.20  
  Purchase #3 $31.94   11.162%   $35.5051   $35.51   $35.50   $35.50  
  Purchase #4 $166.86   6.105%   $177.0468   $177.05   $177.05   $177.00  
  Purchase #5 $67.85   12.721%   $76.4812   $76.48   $76.50   $76.50  
  Purchase #6 $71.85   10.559%   $79.4366   $79.44   $79.45   $79.40  
  Purchase #7 $62.56   6.511%   $66.6333   $66.63   $66.65   $66.60  
  7 purchase totals = $526.98       $574.5149   $574.52   $574.60   $574.40