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 $47.27   5.224%   $49.7394   $49.74   $49.75   $49.70  
  Purchase #2 $211.72   10.865%   $234.7234   $234.72   $234.70   $234.70  
  Purchase #3 $211.81   11.871%   $236.954   $236.95   $236.95   $237.00  
  Purchase #4 $10.72   4.194%   $11.1696   $11.17   $11.15   $11.20  
  Purchase #5 $149.30   5.150%   $156.989   $156.99   $157.00   $157.00  
  Purchase #6 $156.90   12.428%   $176.3995   $176.40   $176.40   $176.40  
  Purchase #7 $27.25   8.820%   $29.6535   $29.65   $29.65   $29.70  
  7 purchase totals = $814.97       $895.6284   $895.62   $895.60   $895.70