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 $62.78   8.858%   $68.3411   $68.34   $68.35   $68.30  
  Purchase #2 $174.95   10.281%   $192.9366   $192.94   $192.95   $192.90  
  Purchase #3 $163.78   4.770%   $171.5923   $171.59   $171.60   $171.60  
  Purchase #4 $98.88   4.502%   $103.3316   $103.33   $103.35   $103.30  
  Purchase #5 $134.86   4.535%   $140.9759   $140.98   $141.00   $141.00  
  Purchase #6 $70.33   13.531%   $79.8464   $79.85   $79.85   $79.80  
  Purchase #7 $69.97   7.734%   $75.3815   $75.38   $75.40   $75.40  
  7 purchase totals = $775.55       $832.4054   $832.41   $832.50   $832.30