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 $82.43   4.764%   $86.357   $86.36   $86.35   $86.40  
  Purchase #2 $72.38   10.143%   $79.7215   $79.72   $79.70   $79.70  
  Purchase #3 $216.86   6.229%   $230.3682   $230.37   $230.35   $230.40  
  Purchase #4 $45.74   11.102%   $50.8181   $50.82   $50.80   $50.80  
  Purchase #5 $190.34   3.635%   $197.2589   $197.26   $197.25   $197.30  
  Purchase #6 $5.54   11.121%   $6.1561   $6.16   $6.15   $6.20  
  Purchase #7 $71.67   3.551%   $74.215   $74.22   $74.20   $74.20  
  7 purchase totals = $684.96       $724.8948   $724.91   $724.80   $725.00