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 $137.72   11.674%   $153.7974   $153.80   $153.80   $153.80  
  Purchase #2 $226.63   6.209%   $240.7015   $240.70   $240.70   $240.70  
  Purchase #3 $130.63   8.820%   $142.1516   $142.15   $142.15   $142.20  
  Purchase #4 $150.53   3.553%   $155.8783   $155.88   $155.90   $155.90  
  Purchase #5 $114.28   13.457%   $129.6587   $129.66   $129.65   $129.70  
  Purchase #6 $6.65   13.731%   $7.5631   $7.56   $7.55   $7.60  
  Purchase #7 $173.42   12.226%   $194.6223   $194.62   $194.60   $194.60  
  7 purchase totals = $939.86       $1,024.3729   $1,024.37   $1,024.35   $1,024.50