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 $68.82   3.617%   $71.3092   $71.31   $71.30   $71.30  
  Purchase #2 $75.78   13.784%   $86.2255   $86.23   $86.25   $86.20  
  Purchase #3 $114.50   13.212%   $129.6277   $129.63   $129.65   $129.60  
  Purchase #4 $158.42   4.515%   $165.5727   $165.57   $165.55   $165.60  
  Purchase #5 $167.64   3.839%   $174.0757   $174.08   $174.10   $174.10  
  Purchase #6 $67.43   3.146%   $69.5513   $69.55   $69.55   $69.60  
  Purchase #7 $43.49   12.128%   $48.7645   $48.76   $48.75   $48.80  
  7 purchase totals = $696.08       $745.1266   $745.13   $745.15   $745.20