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 $227.25   8.768%   $247.1753   $247.18   $247.20   $247.20  
  Purchase #2 $44.58   6.558%   $47.5036   $47.50   $47.50   $47.50  
  Purchase #3 $87.29   9.386%   $95.483   $95.48   $95.50   $95.50  
  Purchase #4 $185.67   10.863%   $205.8393   $205.84   $205.85   $205.80  
  Purchase #5 $194.98   4.800%   $204.339   $204.34   $204.35   $204.30  
  Purchase #6 $128.72   8.324%   $139.4347   $139.43   $139.45   $139.40  
  Purchase #7 $14.67   3.446%   $15.1755   $15.18   $15.20   $15.20  
  7 purchase totals = $883.16       $954.9504   $954.95   $955.05   $954.90