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 $216.73   11.262%   $241.1381   $241.14   $241.15   $241.10  
  Purchase #2 $232.90   10.716%   $257.8576   $257.86   $257.85   $257.90  
  Purchase #3 $37.98   7.855%   $40.9633   $40.96   $40.95   $41.00  
  Purchase #4 $182.71   9.113%   $199.3604   $199.36   $199.35   $199.40  
  Purchase #5 $137.95   8.721%   $149.9806   $149.98   $150.00   $150.00  
  Purchase #6 $123.43   9.191%   $134.7745   $134.77   $134.75   $134.80  
  Purchase #7 $169.77   9.521%   $185.9338   $185.93   $185.95   $185.90  
  7 purchase totals = $1,101.47       $1,210.0083   $1,210.00   $1,210.00   $1,210.10