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 $46.36   13.618%   $52.6733   $52.67   $52.65   $52.70  
  Purchase #2 $230.52   12.396%   $259.0953   $259.10   $259.10   $259.10  
  Purchase #3 $78.41   5.786%   $82.9468   $82.95   $82.95   $82.90  
  Purchase #4 $125.84   7.482%   $135.2553   $135.26   $135.25   $135.30  
  Purchase #5 $140.59   9.614%   $154.1063   $154.11   $154.10   $154.10  
  Purchase #6 $184.78   4.748%   $193.5534   $193.55   $193.55   $193.60  
  Purchase #7 $72.59   12.485%   $81.6529   $81.65   $81.65   $81.70  
  7 purchase totals = $879.09       $959.2833   $959.29   $959.25   $959.40