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 $136.27   13.170%   $154.2168   $154.22   $154.20   $154.20  
  Purchase #2 $156.37   11.630%   $174.5558   $174.56   $174.55   $174.60  
  Purchase #3 $192.56   9.193%   $210.262   $210.26   $210.25   $210.30  
  Purchase #4 $46.36   4.615%   $48.4995   $48.50   $48.50   $48.50  
  Purchase #5 $144.75   11.380%   $161.2226   $161.22   $161.20   $161.20  
  Purchase #6 $144.55   10.133%   $159.1973   $159.20   $159.20   $159.20  
  Purchase #7 $210.27   3.197%   $216.9923   $216.99   $217.00   $217.00  
  7 purchase totals = $1,031.13       $1,124.9463   $1,124.95   $1,124.90   $1,125.00