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 $206.69   13.355%   $234.2934   $234.29   $234.30   $234.30  
  Purchase #2 $155.69   11.195%   $173.1195   $173.12   $173.10   $173.10  
  Purchase #3 $92.80   3.468%   $96.0183   $96.02   $96.00   $96.00  
  Purchase #4 $83.53   10.560%   $92.3508   $92.35   $92.35   $92.40  
  Purchase #5 $166.33   9.551%   $182.2162   $182.22   $182.20   $182.20  
  Purchase #6 $129.29   12.838%   $145.8883   $145.89   $145.90   $145.90  
  Purchase #7 $213.84   4.246%   $222.9196   $222.92   $222.90   $222.90  
  7 purchase totals = $1,048.17       $1,146.8061   $1,146.81   $1,146.75   $1,146.80