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 $212.93   6.726%   $227.2517   $227.25   $227.25   $227.30  
  Purchase #2 $106.48   11.729%   $118.969   $118.97   $118.95   $119.00  
  Purchase #3 $174.73   12.555%   $196.6674   $196.67   $196.65   $196.70  
  Purchase #4 $232.48   6.522%   $247.6423   $247.64   $247.65   $247.60  
  Purchase #5 $194.38   12.711%   $219.0876   $219.09   $219.10   $219.10  
  Purchase #6 $186.49   9.401%   $204.0219   $204.02   $204.00   $204.00  
  Purchase #7 $184.45   4.545%   $192.8333   $192.83   $192.85   $192.80  
  7 purchase totals = $1,291.94       $1,406.4732   $1,406.47   $1,406.45   $1,406.50