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 $108.69   13.372%   $123.224   $123.22   $123.20   $123.20  
  Purchase #2 $156.85   7.549%   $168.6906   $168.69   $168.70   $168.70  
  Purchase #3 $218.93   12.168%   $245.5694   $245.57   $245.55   $245.60  
  Purchase #4 $74.25   4.145%   $77.3277   $77.33   $77.35   $77.30  
  Purchase #5 $73.49   11.443%   $81.8995   $81.90   $81.90   $81.90  
  Purchase #6 $160.36   5.741%   $169.5663   $169.57   $169.55   $169.60  
  Purchase #7 $79.82   6.239%   $84.8   $84.80   $84.80   $84.80  
  7 purchase totals = $872.39       $951.0775   $951.08   $951.05   $951.10