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 $232.96   5.424%   $245.5958   $245.60   $245.60   $245.60  
  Purchase #2 $55.82   11.274%   $62.1131   $62.11   $62.10   $62.10  
  Purchase #3 $13.49   12.439%   $15.168   $15.17   $15.15   $15.20  
  Purchase #4 $155.30   11.420%   $173.0353   $173.04   $173.05   $173.00  
  Purchase #5 $156.49   5.612%   $165.2722   $165.27   $165.25   $165.30  
  Purchase #6 $69.38   4.366%   $72.4091   $72.41   $72.40   $72.40  
  Purchase #7 $11.35   9.289%   $12.4043   $12.40   $12.40   $12.40  
  7 purchase totals = $694.79       $745.9978   $746.00   $745.95   $746.00