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 $246.49   6.772%   $263.1823   $263.18   $263.20   $263.20  
  Purchase #2 $11.55   3.407%   $11.9435   $11.94   $11.95   $11.90  
  Purchase #3 $117.29   6.815%   $125.2833   $125.28   $125.30   $125.30  
  Purchase #4 $205.95   12.815%   $232.3425   $232.34   $232.35   $232.30  
  Purchase #5 $205.39   4.262%   $214.1437   $214.14   $214.15   $214.10  
  Purchase #6 $97.52   13.505%   $110.6901   $110.69   $110.70   $110.70  
  Purchase #7 $5.94   9.334%   $6.4944   $6.49   $6.50   $6.50  
  7 purchase totals = $890.13       $964.0798   $964.06   $964.15   $964.00