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 $59.69   6.296%   $63.4481   $63.45   $63.45   $63.40  
  Purchase #2 $237.65   11.308%   $264.5235   $264.52   $264.50   $264.50  
  Purchase #3 $49.33   5.346%   $51.9672   $51.97   $51.95   $52.00  
  Purchase #4 $197.59   9.491%   $216.3433   $216.34   $216.35   $216.30  
  Purchase #5 $129.61   8.778%   $140.9872   $140.99   $141.00   $141.00  
  Purchase #6 $119.89   4.513%   $125.3006   $125.30   $125.30   $125.30  
  Purchase #7 $64.80   12.134%   $72.6628   $72.66   $72.65   $72.70  
  7 purchase totals = $858.56       $935.2327   $935.23   $935.20   $935.20