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 $217.93   13.333%   $246.9866   $246.99   $247.00   $247.00  
  Purchase #2 $31.57   12.127%   $35.3985   $35.40   $35.40   $35.40  
  Purchase #3 $82.80   4.836%   $86.8042   $86.80   $86.80   $86.80  
  Purchase #4 $208.37   10.458%   $230.1613   $230.16   $230.15   $230.20  
  Purchase #5 $195.36   4.798%   $204.7334   $204.73   $204.75   $204.70  
  Purchase #6 $153.46   10.638%   $169.7851   $169.79   $169.80   $169.80  
  Purchase #7 $9.96   6.203%   $10.5778   $10.58   $10.60   $10.60  
  7 purchase totals = $899.45       $984.4469   $984.45   $984.50   $984.50