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 $189.47   12.245%   $212.6706   $212.67   $212.65   $212.70  
  Purchase #2 $174.63   4.794%   $183.0018   $183.00   $183.00   $183.00  
  Purchase #3 $186.30   4.861%   $195.356   $195.36   $195.35   $195.40  
  Purchase #4 $148.64   3.118%   $153.2746   $153.27   $153.25   $153.30  
  Purchase #5 $221.25   8.800%   $240.72   $240.72   $240.70   $240.70  
  Purchase #6 $198.59   8.611%   $215.6906   $215.69   $215.70   $215.70  
  Purchase #7 $87.25   7.162%   $93.4988   $93.50   $93.50   $93.50  
  7 purchase totals = $1,206.13       $1,294.2124   $1,294.21   $1,294.15   $1,294.30