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 $233.37   6.272%   $248.007   $248.01   $248.00   $248.00  
  Purchase #2 $87.71   11.144%   $97.4844   $97.48   $97.50   $97.50  
  Purchase #3 $54.43   11.788%   $60.8462   $60.85   $60.85   $60.80  
  Purchase #4 $118.88   7.828%   $128.1859   $128.19   $128.20   $128.20  
  Purchase #5 $64.96   9.287%   $70.9928   $70.99   $71.00   $71.00  
  Purchase #6 $53.84   9.814%   $59.1239   $59.12   $59.10   $59.10  
  Purchase #7 $10.41   10.449%   $11.4977   $11.50   $11.50   $11.50  
  7 purchase totals = $623.60       $676.1379   $676.14   $676.15   $676.10