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 $86.82   8.657%   $94.336   $94.34   $94.35   $94.30  
  Purchase #2 $43.84   5.608%   $46.2985   $46.30   $46.30   $46.30  
  Purchase #3 $147.53   7.737%   $158.9444   $158.94   $158.95   $158.90  
  Purchase #4 $23.39   4.386%   $24.4159   $24.42   $24.40   $24.40  
  Purchase #5 $85.39   11.600%   $95.2952   $95.30   $95.30   $95.30  
  Purchase #6 $190.25   6.115%   $201.8838   $201.88   $201.90   $201.90  
  Purchase #7 $169.70   5.219%   $178.5566   $178.56   $178.55   $178.60  
  7 purchase totals = $746.92       $799.7304   $799.74   $799.75   $799.70