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 $96.70   4.167%   $100.7295   $100.73   $100.75   $100.70  
  Purchase #2 $191.30   8.381%   $207.3329   $207.33   $207.35   $207.30  
  Purchase #3 $129.50   8.790%   $140.8831   $140.88   $140.90   $140.90  
  Purchase #4 $210.68   4.813%   $220.82   $220.82   $220.80   $220.80  
  Purchase #5 $11.84   7.659%   $12.7468   $12.75   $12.75   $12.70  
  Purchase #6 $118.44   5.327%   $124.7493   $124.75   $124.75   $124.70  
  Purchase #7 $199.55   13.268%   $226.0263   $226.03   $226.05   $226.00  
  7 purchase totals = $958.01       $1,033.2879   $1,033.29   $1,033.35   $1,033.10