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 $193.72   5.776%   $204.9093   $204.91   $204.90   $204.90  
  Purchase #2 $103.64   7.252%   $111.156   $111.16   $111.15   $111.20  
  Purchase #3 $26.68   11.340%   $29.7055   $29.71   $29.70   $29.70  
  Purchase #4 $228.81   10.182%   $252.1074   $252.11   $252.10   $252.10  
  Purchase #5 $56.77   6.579%   $60.5049   $60.50   $60.50   $60.50  
  Purchase #6 $114.96   13.263%   $130.2071   $130.21   $130.20   $130.20  
  Purchase #7 $216.76   7.791%   $233.6478   $233.65   $233.65   $233.60  
  7 purchase totals = $941.34       $1,022.2380   $1,022.25   $1,022.20   $1,022.20