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 $247.62   8.867%   $269.5765   $269.58   $269.60   $269.60  
  Purchase #2 $51.82   4.154%   $53.9726   $53.97   $53.95   $54.00  
  Purchase #3 $159.65   8.649%   $173.4581   $173.46   $173.45   $173.50  
  Purchase #4 $27.47   8.743%   $29.8717   $29.87   $29.85   $29.90  
  Purchase #5 $94.63   4.577%   $98.9612   $98.96   $98.95   $99.00  
  Purchase #6 $107.46   12.640%   $121.0429   $121.04   $121.05   $121.00  
  Purchase #7 $46.66   3.833%   $48.4485   $48.45   $48.45   $48.40  
  7 purchase totals = $735.31       $795.3315   $795.33   $795.30   $795.40