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 $124.75   13.123%   $141.1209   $141.12   $141.10   $141.10  
  Purchase #2 $176.26   8.666%   $191.5347   $191.53   $191.55   $191.50  
  Purchase #3 $69.77   7.106%   $74.7279   $74.73   $74.75   $74.70  
  Purchase #4 $109.62   9.118%   $119.6152   $119.62   $119.60   $119.60  
  Purchase #5 $91.60   9.532%   $100.3313   $100.33   $100.35   $100.30  
  Purchase #6 $227.55   5.410%   $239.8605   $239.86   $239.85   $239.90  
  Purchase #7 $34.45   4.209%   $35.9   $35.90   $35.90   $35.90  
  7 purchase totals = $834.00       $903.0905   $903.09   $903.10   $903.00