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 $221.80   8.772%   $241.2563   $241.26   $241.25   $241.30  
  Purchase #2 $68.54   3.384%   $70.8594   $70.86   $70.85   $70.90  
  Purchase #3 $6.67   9.559%   $7.3076   $7.31   $7.30   $7.30  
  Purchase #4 $99.48   13.856%   $113.2639   $113.26   $113.25   $113.30  
  Purchase #5 $75.95   12.573%   $85.4992   $85.50   $85.50   $85.50  
  Purchase #6 $238.79   6.431%   $254.1466   $254.15   $254.15   $254.10  
  Purchase #7 $224.53   13.116%   $253.9794   $253.98   $254.00   $254.00  
  7 purchase totals = $935.76       $1,026.3124   $1,026.32   $1,026.30   $1,026.40