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 $23.65   13.278%   $26.7902   $26.79   $26.80   $26.80  
  Purchase #2 $80.51   5.842%   $85.2134   $85.21   $85.20   $85.20  
  Purchase #3 $104.69   3.306%   $108.1511   $108.15   $108.15   $108.20  
  Purchase #4 $212.61   9.697%   $233.2268   $233.23   $233.25   $233.20  
  Purchase #5 $43.31   8.613%   $47.0403   $47.04   $47.05   $47.00  
  Purchase #6 $195.67   9.267%   $213.8027   $213.80   $213.80   $213.80  
  Purchase #7 $15.69   8.637%   $17.0451   $17.05   $17.05   $17.00  
  7 purchase totals = $676.13       $731.2696   $731.27   $731.30   $731.20