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 $226.58   11.514%   $252.6684   $252.67   $252.65   $252.70  
  Purchase #2 $244.32   4.164%   $254.4935   $254.49   $254.50   $254.50  
  Purchase #3 $27.86   7.741%   $30.0166   $30.02   $30.00   $30.00  
  Purchase #4 $237.63   9.140%   $259.3494   $259.35   $259.35   $259.30  
  Purchase #5 $80.73   13.341%   $91.5002   $91.50   $91.50   $91.50  
  Purchase #6 $96.45   6.784%   $102.9932   $102.99   $103.00   $103.00  
  Purchase #7 $213.50   13.797%   $242.9566   $242.96   $242.95   $243.00  
  7 purchase totals = $1,127.07       $1,233.9779   $1,233.98   $1,233.95   $1,234.00