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 $32.38   7.242%   $34.725   $34.73   $34.75   $34.70  
  Purchase #2 $64.50   4.585%   $67.4573   $67.46   $67.45   $67.50  
  Purchase #3 $120.96   3.312%   $124.9662   $124.97   $124.95   $125.00  
  Purchase #4 $121.40   3.213%   $125.3006   $125.30   $125.30   $125.30  
  Purchase #5 $121.47   6.207%   $129.0096   $129.01   $129.00   $129.00  
  Purchase #6 $240.27   7.214%   $257.6031   $257.60   $257.60   $257.60  
  Purchase #7 $41.41   12.379%   $46.5361   $46.54   $46.55   $46.50  
  7 purchase totals = $742.39       $785.5979   $785.61   $785.60   $785.60