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 $211.59   13.874%   $240.946   $240.95   $240.95   $240.90  
  Purchase #2 $164.54   7.674%   $177.1668   $177.17   $177.15   $177.20  
  Purchase #3 $25.79   13.765%   $29.34   $29.34   $29.35   $29.30  
  Purchase #4 $55.71   3.591%   $57.7105   $57.71   $57.70   $57.70  
  Purchase #5 $149.48   6.501%   $159.1977   $159.20   $159.20   $159.20  
  Purchase #6 $187.84   13.486%   $213.1721   $213.17   $213.15   $213.20  
  Purchase #7 $46.96   5.330%   $49.463   $49.46   $49.45   $49.50  
  7 purchase totals = $841.91       $926.9961   $927.00   $926.95   $927.00