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 $61.86   4.419%   $64.5936   $64.59   $64.60   $64.60  
  Purchase #2 $226.50   5.567%   $239.1093   $239.11   $239.10   $239.10  
  Purchase #3 $46.27   4.383%   $48.298   $48.30   $48.30   $48.30  
  Purchase #4 $32.82   6.150%   $34.8384   $34.84   $34.85   $34.80  
  Purchase #5 $99.50   12.112%   $111.5514   $111.55   $111.55   $111.60  
  Purchase #6 $134.99   9.570%   $147.9085   $147.91   $147.90   $147.90  
  Purchase #7 $123.33   4.790%   $129.2375   $129.24   $129.25   $129.20  
  7 purchase totals = $725.27       $775.5367   $775.54   $775.55   $775.50