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 $232.75   13.495%   $264.1596   $264.16   $264.15   $264.20  
  Purchase #2 $175.33   11.143%   $194.867   $194.87   $194.85   $194.90  
  Purchase #3 $35.28   7.730%   $38.0071   $38.01   $38.00   $38.00  
  Purchase #4 $48.67   6.457%   $51.8126   $51.81   $51.80   $51.80  
  Purchase #5 $238.52   11.722%   $266.4793   $266.48   $266.50   $266.50  
  Purchase #6 $18.81   8.361%   $20.3827   $20.38   $20.40   $20.40  
  Purchase #7 $135.87   8.168%   $146.9679   $146.97   $146.95   $147.00  
  7 purchase totals = $885.23       $982.6762   $982.68   $982.65   $982.80