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 $248.73   13.152%   $281.443   $281.44   $281.45   $281.40  
  Purchase #2 $86.98   5.737%   $91.97   $91.97   $91.95   $92.00  
  Purchase #3 $187.39   7.821%   $202.0458   $202.05   $202.05   $202.00  
  Purchase #4 $5.94   9.308%   $6.4929   $6.49   $6.50   $6.50  
  Purchase #5 $70.93   4.365%   $74.0261   $74.03   $74.05   $74.00  
  Purchase #6 $185.74   7.817%   $200.2593   $200.26   $200.25   $200.30  
  Purchase #7 $126.44   11.366%   $140.8112   $140.81   $140.80   $140.80  
  7 purchase totals = $912.15       $997.0483   $997.05   $997.05   $997.00