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 $58.77   12.535%   $66.1368   $66.14   $66.15   $66.10  
  Purchase #2 $117.71   5.862%   $124.6102   $124.61   $124.60   $124.60  
  Purchase #3 $87.98   8.132%   $95.1345   $95.13   $95.15   $95.10  
  Purchase #4 $247.63   4.666%   $259.1844   $259.18   $259.20   $259.20  
  Purchase #5 $242.52   4.293%   $252.9314   $252.93   $252.95   $252.90  
  Purchase #6 $106.53   11.701%   $118.9951   $119.00   $119.00   $119.00  
  Purchase #7 $45.68   8.562%   $49.5911   $49.59   $49.60   $49.60  
  7 purchase totals = $906.82       $966.5835   $966.58   $966.65   $966.50