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 $68.73   3.111%   $70.8682   $70.87   $70.85   $70.90  
  Purchase #2 $209.47   9.254%   $228.8544   $228.85   $228.85   $228.90  
  Purchase #3 $25.75   13.833%   $29.312   $29.31   $29.30   $29.30  
  Purchase #4 $151.41   11.774%   $169.237   $169.24   $169.25   $169.20  
  Purchase #5 $213.64   10.701%   $236.5016   $236.50   $236.50   $236.50  
  Purchase #6 $161.75   13.386%   $183.4019   $183.40   $183.40   $183.40  
  Purchase #7 $133.94   11.546%   $149.4047   $149.40   $149.40   $149.40  
  7 purchase totals = $964.69       $1,067.5798   $1,067.57   $1,067.55   $1,067.60