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 $147.54   13.454%   $167.39   $167.39   $167.40   $167.40  
  Purchase #2 $78.53   3.404%   $81.2032   $81.20   $81.20   $81.20  
  Purchase #3 $162.63   13.181%   $184.0663   $184.07   $184.05   $184.10  
  Purchase #4 $131.83   13.301%   $149.3647   $149.36   $149.35   $149.40  
  Purchase #5 $36.82   7.497%   $39.5804   $39.58   $39.60   $39.60  
  Purchase #6 $22.80   8.162%   $24.6609   $24.66   $24.65   $24.70  
  Purchase #7 $61.41   10.328%   $67.7524   $67.75   $67.75   $67.80  
  7 purchase totals = $641.56       $714.0179   $714.01   $714.00   $714.20