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 $36.57   4.505%   $38.2175   $38.22   $38.20   $38.20  
  Purchase #2 $27.66   9.430%   $30.2683   $30.27   $30.25   $30.30  
  Purchase #3 $26.74   7.156%   $28.6535   $28.65   $28.65   $28.70  
  Purchase #4 $82.58   9.443%   $90.378   $90.38   $90.40   $90.40  
  Purchase #5 $66.85   10.781%   $74.0571   $74.06   $74.05   $74.10  
  Purchase #6 $45.43   3.353%   $46.9533   $46.95   $46.95   $47.00  
  Purchase #7 $32.73   6.590%   $34.8869   $34.89   $34.90   $34.90  
  7 purchase totals = $318.56       $343.4146   $343.42   $343.40   $343.60