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 $205.82   9.107%   $224.564   $224.56   $224.55   $224.60  
  Purchase #2 $53.78   6.277%   $57.1558   $57.16   $57.15   $57.20  
  Purchase #3 $94.81   3.683%   $98.3019   $98.30   $98.30   $98.30  
  Purchase #4 $188.30   3.628%   $195.1315   $195.13   $195.15   $195.10  
  Purchase #5 $165.93   5.466%   $174.9997   $175.00   $175.00   $175.00  
  Purchase #6 $241.71   7.458%   $259.7367   $259.74   $259.75   $259.70  
  Purchase #7 $191.97   7.253%   $205.8936   $205.89   $205.90   $205.90  
  7 purchase totals = $1,142.32       $1,215.7832   $1,215.78   $1,215.80   $1,215.80