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 $59.95   5.161%   $63.044   $63.04   $63.05   $63.00  
  Purchase #2 $108.51   8.288%   $117.5033   $117.50   $117.50   $117.50  
  Purchase #3 $210.38   11.552%   $234.6831   $234.68   $234.70   $234.70  
  Purchase #4 $77.77   8.549%   $84.4186   $84.42   $84.40   $84.40  
  Purchase #5 $147.65   4.445%   $154.213   $154.21   $154.20   $154.20  
  Purchase #6 $21.93   4.418%   $22.8989   $22.90   $22.90   $22.90  
  Purchase #7 $132.37   11.834%   $148.0347   $148.03   $148.05   $148.00  
  7 purchase totals = $758.56       $824.7956   $824.78   $824.80   $824.70