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 $230.57   13.854%   $262.5132   $262.51   $262.50   $262.50  
  Purchase #2 $117.29   10.530%   $129.6406   $129.64   $129.65   $129.60  
  Purchase #3 $177.39   4.703%   $185.7327   $185.73   $185.75   $185.70  
  Purchase #4 $156.93   7.105%   $168.0799   $168.08   $168.10   $168.10  
  Purchase #5 $201.53   10.344%   $222.3763   $222.38   $222.40   $222.40  
  Purchase #6 $15.45   8.816%   $16.8121   $16.81   $16.80   $16.80  
  Purchase #7 $56.80   13.221%   $64.3095   $64.31   $64.30   $64.30  
  7 purchase totals = $955.96       $1,049.4643   $1,049.46   $1,049.50   $1,049.40