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 $241.59   8.592%   $262.3474   $262.35   $262.35   $262.30  
  Purchase #2 $44.99   13.431%   $51.0326   $51.03   $51.05   $51.00  
  Purchase #3 $80.63   4.230%   $84.0406   $84.04   $84.05   $84.00  
  Purchase #4 $95.83   8.284%   $103.7686   $103.77   $103.75   $103.80  
  Purchase #5 $118.54   5.363%   $124.8973   $124.90   $124.90   $124.90  
  Purchase #6 $122.80   12.863%   $138.5958   $138.60   $138.60   $138.60  
  Purchase #7 $69.25   4.415%   $72.3074   $72.31   $72.30   $72.30  
  7 purchase totals = $773.63       $836.9897   $837.00   $837.00   $836.90