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 $223.52   13.626%   $253.9768   $253.98   $254.00   $254.00  
  Purchase #2 $108.38   13.716%   $123.2454   $123.25   $123.25   $123.20  
  Purchase #3 $35.81   4.277%   $37.3416   $37.34   $37.35   $37.30  
  Purchase #4 $206.36   8.633%   $224.1751   $224.18   $224.20   $224.20  
  Purchase #5 $37.28   7.542%   $40.0917   $40.09   $40.10   $40.10  
  Purchase #6 $184.50   7.305%   $197.9777   $197.98   $198.00   $198.00  
  Purchase #7 $146.27   7.508%   $157.252   $157.25   $157.25   $157.30  
  7 purchase totals = $942.12       $1,034.0603   $1,034.07   $1,034.15   $1,034.10