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 $234.51   5.333%   $247.0164   $247.02   $247.00   $247.00  
  Purchase #2 $243.53   5.383%   $256.6392   $256.64   $256.65   $256.60  
  Purchase #3 $168.91   9.677%   $185.2554   $185.26   $185.25   $185.30  
  Purchase #4 $201.40   3.706%   $208.8639   $208.86   $208.85   $208.90  
  Purchase #5 $172.99   12.809%   $195.1483   $195.15   $195.15   $195.10  
  Purchase #6 $250.41   6.490%   $266.6616   $266.66   $266.65   $266.70  
  Purchase #7 $22.30   6.580%   $23.7673   $23.77   $23.75   $23.80  
  7 purchase totals = $1,294.05       $1,383.3521   $1,383.36   $1,383.30   $1,383.40