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 $236.94   10.510%   $261.8424   $261.84   $261.85   $261.80  
  Purchase #2 $98.46   6.868%   $105.2222   $105.22   $105.20   $105.20  
  Purchase #3 $172.70   6.130%   $183.2865   $183.29   $183.30   $183.30  
  Purchase #4 $174.37   12.662%   $196.4487   $196.45   $196.45   $196.40  
  Purchase #5 $168.67   4.437%   $176.1539   $176.15   $176.15   $176.20  
  Purchase #6 $43.30   8.219%   $46.8588   $46.86   $46.85   $46.90  
  Purchase #7 $52.82   8.265%   $57.1856   $57.19   $57.20   $57.20  
  7 purchase totals = $947.26       $1,026.9981   $1,027.00   $1,027.00   $1,027.00