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 $247.57   7.769%   $266.8037   $266.80   $266.80   $266.80  
  Purchase #2 $159.71   3.717%   $165.6464   $165.65   $165.65   $165.60  
  Purchase #3 $167.83   3.704%   $174.0464   $174.05   $174.05   $174.00  
  Purchase #4 $24.89   4.422%   $25.9906   $25.99   $26.00   $26.00  
  Purchase #5 $12.62   11.874%   $14.1185   $14.12   $14.10   $14.10  
  Purchase #6 $22.56   4.161%   $23.4987   $23.50   $23.50   $23.50  
  Purchase #7 $169.98   13.478%   $192.8899   $192.89   $192.90   $192.90  
  7 purchase totals = $805.16       $862.9942   $863.00   $863.00   $862.90