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 $65.66   6.164%   $69.7073   $69.71   $69.70   $69.70  
  Purchase #2 $243.67   11.457%   $271.5873   $271.59   $271.60   $271.60  
  Purchase #3 $166.36   11.836%   $186.0504   $186.05   $186.05   $186.10  
  Purchase #4 $214.47   10.276%   $236.5089   $236.51   $236.50   $236.50  
  Purchase #5 $83.28   4.842%   $87.3124   $87.31   $87.30   $87.30  
  Purchase #6 $221.96   9.118%   $242.1983   $242.20   $242.20   $242.20  
  Purchase #7 $133.31   8.723%   $144.9386   $144.94   $144.95   $144.90  
  7 purchase totals = $1,128.71       $1,238.3032   $1,238.31   $1,238.30   $1,238.30