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 $88.83   8.853%   $96.6941   $96.69   $96.70   $96.70  
  Purchase #2 $235.75   6.601%   $251.3119   $251.31   $251.30   $251.30  
  Purchase #3 $85.88   4.265%   $89.5428   $89.54   $89.55   $89.50  
  Purchase #4 $157.56   3.265%   $162.7043   $162.70   $162.70   $162.70  
  Purchase #5 $111.40   9.769%   $122.2827   $122.28   $122.30   $122.30  
  Purchase #6 $14.79   11.227%   $16.4505   $16.45   $16.45   $16.50  
  Purchase #7 $93.84   4.339%   $97.9117   $97.91   $97.90   $97.90  
  7 purchase totals = $788.05       $836.8980   $836.88   $836.90   $836.90