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 $58.99   13.460%   $66.9301   $66.93   $66.95   $66.90  
  Purchase #2 $232.57   13.659%   $264.3367   $264.34   $264.35   $264.30  
  Purchase #3 $59.73   5.786%   $63.186   $63.19   $63.20   $63.20  
  Purchase #4 $210.65   10.628%   $233.0379   $233.04   $233.05   $233.00  
  Purchase #5 $191.71   11.504%   $213.7643   $213.76   $213.75   $213.80  
  Purchase #6 $165.52   6.747%   $176.6876   $176.69   $176.70   $176.70  
  Purchase #7 $204.40   7.608%   $219.9508   $219.95   $219.95   $220.00  
  7 purchase totals = $1,123.57       $1,237.8934   $1,237.90   $1,237.95   $1,237.90