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 $114.82   10.706%   $127.1126   $127.11   $127.10   $127.10  
  Purchase #2 $93.74   10.235%   $103.3343   $103.33   $103.35   $103.30  
  Purchase #3 $111.57   8.534%   $121.0914   $121.09   $121.10   $121.10  
  Purchase #4 $101.26   7.199%   $108.5497   $108.55   $108.55   $108.50  
  Purchase #5 $244.45   11.313%   $272.1046   $272.10   $272.10   $272.10  
  Purchase #6 $158.88   5.841%   $168.1602   $168.16   $168.15   $168.20  
  Purchase #7 $69.99   8.572%   $75.9895   $75.99   $76.00   $76.00  
  7 purchase totals = $894.71       $976.3423   $976.33   $976.35   $976.30