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 $113.53   5.385%   $119.6436   $119.64   $119.65   $119.60  
  Purchase #2 $122.78   9.353%   $134.2636   $134.26   $134.25   $134.30  
  Purchase #3 $49.43   6.165%   $52.4774   $52.48   $52.50   $52.50  
  Purchase #4 $144.32   6.792%   $154.1222   $154.12   $154.10   $154.10  
  Purchase #5 $168.50   3.405%   $174.2374   $174.24   $174.25   $174.20  
  Purchase #6 $32.55   13.119%   $36.8202   $36.82   $36.80   $36.80  
  Purchase #7 $142.82   10.773%   $158.206   $158.21   $158.20   $158.20  
  7 purchase totals = $773.93       $829.7704   $829.77   $829.75   $829.70