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 $140.38   8.712%   $152.6099   $152.61   $152.60   $152.60  
  Purchase #2 $215.98   11.307%   $240.4009   $240.40   $240.40   $240.40  
  Purchase #3 $22.71   13.198%   $25.7073   $25.71   $25.70   $25.70  
  Purchase #4 $106.99   8.463%   $116.0446   $116.04   $116.05   $116.00  
  Purchase #5 $107.92   8.117%   $116.6799   $116.68   $116.70   $116.70  
  Purchase #6 $211.38   5.728%   $223.4878   $223.49   $223.50   $223.50  
  Purchase #7 $122.68   10.598%   $135.6816   $135.68   $135.70   $135.70  
  7 purchase totals = $928.04       $1,010.6120   $1,010.61   $1,010.65   $1,010.60