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 $130.85   12.182%   $146.7901   $146.79   $146.80   $146.80  
  Purchase #2 $212.76   13.356%   $241.1762   $241.18   $241.20   $241.20  
  Purchase #3 $199.91   12.226%   $224.351   $224.35   $224.35   $224.40  
  Purchase #4 $174.88   7.118%   $187.328   $187.33   $187.35   $187.30  
  Purchase #5 $60.83   13.782%   $69.2136   $69.21   $69.20   $69.20  
  Purchase #6 $121.25   13.355%   $137.4429   $137.44   $137.45   $137.40  
  Purchase #7 $54.81   6.655%   $58.4576   $58.46   $58.45   $58.50  
  7 purchase totals = $955.29       $1,064.7594   $1,064.76   $1,064.80   $1,064.80