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 $52.74   10.344%   $58.1954   $58.20   $58.20   $58.20  
  Purchase #2 $150.29   9.757%   $164.9538   $164.95   $164.95   $165.00  
  Purchase #3 $106.25   12.844%   $119.8968   $119.90   $119.90   $119.90  
  Purchase #4 $114.67   9.814%   $125.9237   $125.92   $125.90   $125.90  
  Purchase #5 $180.43   13.828%   $205.3799   $205.38   $205.40   $205.40  
  Purchase #6 $158.67   12.434%   $178.399   $178.40   $178.40   $178.40  
  Purchase #7 $166.61   12.317%   $187.1314   $187.13   $187.15   $187.10  
  7 purchase totals = $929.66       $1,039.8800   $1,039.88   $1,039.90   $1,039.90