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 $204.57   10.865%   $226.7965   $226.80   $226.80   $226.80  
  Purchase #2 $72.79   5.181%   $76.5612   $76.56   $76.55   $76.60  
  Purchase #3 $242.32   5.498%   $255.6428   $255.64   $255.65   $255.60  
  Purchase #4 $143.45   8.809%   $156.0865   $156.09   $156.10   $156.10  
  Purchase #5 $218.86   7.252%   $234.7317   $234.73   $234.75   $234.70  
  Purchase #6 $156.55   8.207%   $169.3981   $169.40   $169.40   $169.40  
  Purchase #7 $235.49   6.180%   $250.0433   $250.04   $250.05   $250.00  
  7 purchase totals = $1,274.03       $1,369.2601   $1,369.26   $1,369.30   $1,369.20