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 $60.57   12.282%   $68.0092   $68.01   $68.00   $68.00  
  Purchase #2 $235.40   11.116%   $261.5671   $261.57   $261.55   $261.60  
  Purchase #3 $75.34   8.787%   $81.9601   $81.96   $81.95   $82.00  
  Purchase #4 $31.42   4.184%   $32.7346   $32.73   $32.75   $32.70  
  Purchase #5 $144.73   3.519%   $149.823   $149.82   $149.80   $149.80  
  Purchase #6 $189.46   13.458%   $214.9575   $214.96   $214.95   $215.00  
  Purchase #7 $7.27   10.394%   $8.0256   $8.03   $8.05   $8.00  
  7 purchase totals = $744.19       $817.0771   $817.08   $817.05   $817.10