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 $221.65   3.580%   $229.5851   $229.59   $229.60   $229.60  
  Purchase #2 $137.28   4.679%   $143.7033   $143.70   $143.70   $143.70  
  Purchase #3 $22.92   3.576%   $23.7396   $23.74   $23.75   $23.70  
  Purchase #4 $247.39   7.758%   $266.5825   $266.58   $266.60   $266.60  
  Purchase #5 $168.85   3.132%   $174.1384   $174.14   $174.15   $174.10  
  Purchase #6 $136.92   9.847%   $150.4025   $150.40   $150.40   $150.40  
  Purchase #7 $30.58   6.229%   $32.4848   $32.48   $32.50   $32.50  
  7 purchase totals = $965.59       $1,020.6362   $1,020.63   $1,020.70   $1,020.60