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 $52.61   8.769%   $57.2234   $57.22   $57.20   $57.20  
  Purchase #2 $228.73   4.806%   $239.7228   $239.72   $239.70   $239.70  
  Purchase #3 $108.56   9.685%   $119.074   $119.07   $119.05   $119.10  
  Purchase #4 $56.30   13.692%   $64.0086   $64.01   $64.00   $64.00  
  Purchase #5 $6.56   5.666%   $6.9317   $6.93   $6.95   $6.90  
  Purchase #6 $189.55   10.576%   $209.5968   $209.60   $209.60   $209.60  
  Purchase #7 $111.52   13.802%   $126.912   $126.91   $126.90   $126.90  
  7 purchase totals = $753.83       $823.4693   $823.46   $823.40   $823.40