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 $135.96   12.673%   $153.1902   $153.19   $153.20   $153.20  
  Purchase #2 $227.52   6.208%   $241.6444   $241.64   $241.65   $241.60  
  Purchase #3 $75.82   12.235%   $85.0966   $85.10   $85.10   $85.10  
  Purchase #4 $248.63   4.823%   $260.6214   $260.62   $260.60   $260.60  
  Purchase #5 $13.82   8.175%   $14.9498   $14.95   $14.95   $14.90  
  Purchase #6 $135.38   12.342%   $152.0886   $152.09   $152.10   $152.10  
  Purchase #7 $55.34   8.252%   $59.9067   $59.91   $59.90   $59.90  
  7 purchase totals = $892.47       $967.4977   $967.50   $967.50   $967.40