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 $112.64   11.268%   $125.3323   $125.33   $125.35   $125.30  
  Purchase #2 $185.95   8.384%   $201.54   $201.54   $201.55   $201.50  
  Purchase #3 $153.83   8.754%   $167.2963   $167.30   $167.30   $167.30  
  Purchase #4 $87.80   11.575%   $97.9629   $97.96   $97.95   $98.00  
  Purchase #5 $114.29   7.618%   $122.9966   $123.00   $123.00   $123.00  
  Purchase #6 $83.96   4.798%   $87.9884   $87.99   $88.00   $88.00  
  Purchase #7 $176.59   5.177%   $185.7321   $185.73   $185.75   $185.70  
  7 purchase totals = $915.06       $988.8486   $988.85   $988.90   $988.80