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 $99.84   4.665%   $104.4975   $104.50   $104.50   $104.50  
  Purchase #2 $91.61   12.310%   $102.8872   $102.89   $102.90   $102.90  
  Purchase #3 $15.83   7.283%   $16.9829   $16.98   $17.00   $17.00  
  Purchase #4 $9.54   4.669%   $9.9854   $9.99   $10.00   $10.00  
  Purchase #5 $87.38   9.237%   $95.4513   $95.45   $95.45   $95.50  
  Purchase #6 $46.72   8.787%   $50.8253   $50.83   $50.85   $50.80  
  Purchase #7 $97.97   9.107%   $106.8921   $106.89   $106.90   $106.90  
  7 purchase totals = $448.89       $487.5217   $487.53   $487.60   $487.60