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 $218.42   6.673%   $232.9952   $233.00   $233.00   $233.00  
  Purchase #2 $33.84   12.359%   $38.0223   $38.02   $38.00   $38.00  
  Purchase #3 $60.39   5.703%   $63.834   $63.83   $63.85   $63.80  
  Purchase #4 $91.70   9.193%   $100.13   $100.13   $100.15   $100.10  
  Purchase #5 $42.53   12.175%   $47.708   $47.71   $47.70   $47.70  
  Purchase #6 $96.78   6.153%   $102.7349   $102.73   $102.75   $102.70  
  Purchase #7 $146.53   12.782%   $165.2595   $165.26   $165.25   $165.30  
  7 purchase totals = $690.19       $750.6839   $750.68   $750.70   $750.60