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 $115.68   10.126%   $127.3938   $127.39   $127.40   $127.40  
  Purchase #2 $13.49   7.829%   $14.5461   $14.55   $14.55   $14.50  
  Purchase #3 $153.39   9.309%   $167.6691   $167.67   $167.65   $167.70  
  Purchase #4 $93.25   11.635%   $104.0996   $104.10   $104.10   $104.10  
  Purchase #5 $23.87   10.411%   $26.3551   $26.36   $26.35   $26.40  
  Purchase #6 $193.26   12.465%   $217.3499   $217.35   $217.35   $217.30  
  Purchase #7 $61.52   11.363%   $68.5105   $68.51   $68.50   $68.50  
  7 purchase totals = $654.46       $725.9241   $725.93   $725.90   $725.90