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 $67.41   7.303%   $72.333   $72.33   $72.35   $72.30  
  Purchase #2 $18.98   6.870%   $20.2839   $20.28   $20.30   $20.30  
  Purchase #3 $218.56   11.401%   $243.478   $243.48   $243.50   $243.50  
  Purchase #4 $23.41   12.523%   $26.3416   $26.34   $26.35   $26.30  
  Purchase #5 $74.80   5.820%   $79.1534   $79.15   $79.15   $79.20  
  Purchase #6 $137.77   9.650%   $151.0648   $151.06   $151.05   $151.10  
  Purchase #7 $127.95   4.149%   $133.2586   $133.26   $133.25   $133.30  
  7 purchase totals = $668.88       $725.9133   $725.90   $725.95   $726.00