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 $52.79   12.201%   $59.2309   $59.23   $59.25   $59.20  
  Purchase #2 $82.64   12.502%   $92.9717   $92.97   $92.95   $93.00  
  Purchase #3 $72.44   13.701%   $82.365   $82.37   $82.35   $82.40  
  Purchase #4 $223.25   5.783%   $236.1605   $236.16   $236.15   $236.20  
  Purchase #5 $87.33   12.445%   $98.1982   $98.20   $98.20   $98.20  
  Purchase #6 $71.86   8.566%   $78.0155   $78.02   $78.00   $78.00  
  Purchase #7 $193.61   12.732%   $218.2604   $218.26   $218.25   $218.30  
  7 purchase totals = $783.92       $865.2022   $865.21   $865.15   $865.30