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 $206.92   11.541%   $230.8006   $230.80   $230.80   $230.80  
  Purchase #2 $143.27   9.282%   $156.5683   $156.57   $156.55   $156.60  
  Purchase #3 $83.41   3.570%   $86.3877   $86.39   $86.40   $86.40  
  Purchase #4 $173.50   7.243%   $186.0666   $186.07   $186.05   $186.10  
  Purchase #5 $183.49   12.521%   $206.4648   $206.46   $206.45   $206.50  
  Purchase #6 $134.32   11.535%   $149.8138   $149.81   $149.80   $149.80  
  Purchase #7 $26.57   7.136%   $28.466   $28.47   $28.45   $28.50  
  7 purchase totals = $951.48       $1,044.5678   $1,044.57   $1,044.50   $1,044.70