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 $35.71   7.159%   $38.2665   $38.27   $38.25   $38.30  
  Purchase #2 $218.99   5.195%   $230.3665   $230.37   $230.35   $230.40  
  Purchase #3 $240.80   3.303%   $248.7536   $248.75   $248.75   $248.80  
  Purchase #4 $60.97   8.182%   $65.9586   $65.96   $65.95   $66.00  
  Purchase #5 $71.36   5.650%   $75.3918   $75.39   $75.40   $75.40  
  Purchase #6 $109.33   9.285%   $119.4813   $119.48   $119.50   $119.50  
  Purchase #7 $160.29   6.347%   $170.4636   $170.46   $170.45   $170.50  
  7 purchase totals = $897.45       $948.6819   $948.68   $948.65   $948.90