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 $211.53   3.632%   $219.2128   $219.21   $219.20   $219.20  
  Purchase #2 $173.82   13.670%   $197.5812   $197.58   $197.60   $197.60  
  Purchase #3 $55.70   5.872%   $58.9707   $58.97   $58.95   $59.00  
  Purchase #4 $220.61   6.588%   $235.1438   $235.14   $235.15   $235.10  
  Purchase #5 $247.48   5.829%   $261.9056   $261.91   $261.90   $261.90  
  Purchase #6 $223.41   5.496%   $235.6886   $235.69   $235.70   $235.70  
  Purchase #7 $31.44   9.491%   $34.424   $34.42   $34.40   $34.40  
  7 purchase totals = $1,163.99       $1,242.9267   $1,242.92   $1,242.90   $1,242.90