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 $249.60   10.188%   $275.0292   $275.03   $275.05   $275.00  
  Purchase #2 $64.92   6.645%   $69.2339   $69.23   $69.25   $69.20  
  Purchase #3 $16.58   11.628%   $18.5079   $18.51   $18.50   $18.50  
  Purchase #4 $204.54   5.427%   $215.6404   $215.64   $215.65   $215.60  
  Purchase #5 $156.31   8.553%   $169.6792   $169.68   $169.70   $169.70  
  Purchase #6 $135.32   6.325%   $143.879   $143.88   $143.90   $143.90  
  Purchase #7 $70.81   4.731%   $74.16   $74.16   $74.15   $74.20  
  7 purchase totals = $898.08       $966.1296   $966.13   $966.20   $966.10