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 $231.58   9.682%   $254.0016   $254.00   $254.00   $254.00  
  Purchase #2 $218.92   12.799%   $246.9396   $246.94   $246.95   $246.90  
  Purchase #3 $109.64   6.538%   $116.8083   $116.81   $116.80   $116.80  
  Purchase #4 $215.86   12.181%   $242.1539   $242.15   $242.15   $242.20  
  Purchase #5 $94.51   4.294%   $98.5683   $98.57   $98.55   $98.60  
  Purchase #6 $30.92   4.569%   $32.3327   $32.33   $32.35   $32.30  
  Purchase #7 $211.51   4.342%   $220.6938   $220.69   $220.70   $220.70  
  7 purchase totals = $1,112.94       $1,211.4982   $1,211.49   $1,211.50   $1,211.50