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 $175.37   11.377%   $195.3218   $195.32   $195.30   $195.30  
  Purchase #2 $45.36   9.597%   $49.7132   $49.71   $49.70   $49.70  
  Purchase #3 $223.98   5.297%   $235.8442   $235.84   $235.85   $235.80  
  Purchase #4 $51.90   5.527%   $54.7685   $54.77   $54.75   $54.80  
  Purchase #5 $130.62   4.253%   $136.1753   $136.18   $136.20   $136.20  
  Purchase #6 $182.77   12.657%   $205.9032   $205.90   $205.90   $205.90  
  Purchase #7 $132.59   3.152%   $136.7692   $136.77   $136.75   $136.80  
  7 purchase totals = $942.59       $1,014.4954   $1,014.49   $1,014.45   $1,014.50