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 $56.34   12.140%   $63.1797   $63.18   $63.20   $63.20  
  Purchase #2 $208.45   13.549%   $236.6929   $236.69   $236.70   $236.70  
  Purchase #3 $154.70   12.315%   $173.7513   $173.75   $173.75   $173.80  
  Purchase #4 $240.39   5.668%   $254.0153   $254.02   $254.00   $254.00  
  Purchase #5 $54.66   10.163%   $60.2151   $60.22   $60.20   $60.20  
  Purchase #6 $183.91   9.674%   $201.7015   $201.70   $201.70   $201.70  
  Purchase #7 $74.98   9.146%   $81.8377   $81.84   $81.85   $81.80  
  7 purchase totals = $973.43       $1,071.3935   $1,071.40   $1,071.40   $1,071.40