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 $23.53   10.313%   $25.9566   $25.96   $25.95   $26.00  
  Purchase #2 $131.65   9.752%   $144.4885   $144.49   $144.50   $144.50  
  Purchase #3 $13.41   7.170%   $14.3715   $14.37   $14.35   $14.40  
  Purchase #4 $193.25   8.174%   $209.0463   $209.05   $209.05   $209.00  
  Purchase #5 $172.38   13.122%   $194.9997   $195.00   $195.00   $195.00  
  Purchase #6 $5.83   11.669%   $6.5103   $6.51   $6.50   $6.50  
  Purchase #7 $16.64   4.463%   $17.3826   $17.38   $17.40   $17.40  
  7 purchase totals = $556.69       $612.7555   $612.76   $612.75   $612.80