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 $86.29   13.504%   $97.9426   $97.94   $97.95   $97.90  
  Purchase #2 $163.37   3.135%   $168.4916   $168.49   $168.50   $168.50  
  Purchase #3 $136.31   9.563%   $149.3453   $149.35   $149.35   $149.30  
  Purchase #4 $224.53   11.160%   $249.5875   $249.59   $249.60   $249.60  
  Purchase #5 $119.78   5.624%   $126.5164   $126.52   $126.50   $126.50  
  Purchase #6 $14.38   13.446%   $16.3135   $16.31   $16.30   $16.30  
  Purchase #7 $181.62   11.606%   $202.6988   $202.70   $202.70   $202.70  
  7 purchase totals = $926.28       $1,010.8957   $1,010.90   $1,010.90   $1,010.80