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 $174.97   8.397%   $189.6622   $189.66   $189.65   $189.70  
  Purchase #2 $250.47   11.121%   $278.3248   $278.32   $278.30   $278.30  
  Purchase #3 $35.38   9.302%   $38.671   $38.67   $38.65   $38.70  
  Purchase #4 $220.81   11.725%   $246.7   $246.70   $246.70   $246.70  
  Purchase #5 $216.62   6.601%   $230.9191   $230.92   $230.90   $230.90  
  Purchase #6 $68.87   7.874%   $74.2928   $74.29   $74.30   $74.30  
  Purchase #7 $237.68   3.547%   $246.1105   $246.11   $246.10   $246.10  
  7 purchase totals = $1,204.80       $1,304.6804   $1,304.67   $1,304.60   $1,304.70