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 $32.68   6.145%   $34.6882   $34.69   $34.70   $34.70  
  Purchase #2 $168.70   4.463%   $176.2291   $176.23   $176.25   $176.20  
  Purchase #3 $96.48   12.705%   $108.7378   $108.74   $108.75   $108.70  
  Purchase #4 $45.53   9.732%   $49.961   $49.96   $49.95   $50.00  
  Purchase #5 $52.60   6.499%   $56.0185   $56.02   $56.00   $56.00  
  Purchase #6 $123.34   9.267%   $134.7699   $134.77   $134.75   $134.80  
  Purchase #7 $56.28   10.193%   $62.0166   $62.02   $62.00   $62.00  
  7 purchase totals = $575.61       $622.4211   $622.43   $622.40   $622.40