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 $208.74   10.327%   $230.2966   $230.30   $230.30   $230.30  
  Purchase #2 $241.45   7.245%   $258.9431   $258.94   $258.95   $258.90  
  Purchase #3 $96.63   10.273%   $106.5568   $106.56   $106.55   $106.60  
  Purchase #4 $151.61   3.105%   $156.3175   $156.32   $156.30   $156.30  
  Purchase #5 $238.53   6.755%   $254.6427   $254.64   $254.65   $254.60  
  Purchase #6 $109.93   4.672%   $115.0659   $115.07   $115.05   $115.10  
  Purchase #7 $210.56   7.550%   $226.4573   $226.46   $226.45   $226.50  
  7 purchase totals = $1,257.45       $1,348.2799   $1,348.29   $1,348.25   $1,348.30