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 $206.35   13.754%   $234.7314   $234.73   $234.75   $234.70  
  Purchase #2 $232.88   10.324%   $256.9225   $256.92   $256.90   $256.90  
  Purchase #3 $206.52   7.643%   $222.3043   $222.30   $222.30   $222.30  
  Purchase #4 $23.34   12.583%   $26.2769   $26.28   $26.30   $26.30  
  Purchase #5 $221.29   12.800%   $249.6151   $249.62   $249.60   $249.60  
  Purchase #6 $111.83   12.332%   $125.6209   $125.62   $125.60   $125.60  
  Purchase #7 $183.36   9.641%   $201.0377   $201.04   $201.05   $201.00  
  7 purchase totals = $1,185.57       $1,316.5088   $1,316.51   $1,316.50   $1,316.40