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 $55.94   10.833%   $62   $62.00   $62.00   $62.00  
  Purchase #2 $120.84   7.660%   $130.0963   $130.10   $130.10   $130.10  
  Purchase #3 $66.69   4.716%   $69.8351   $69.84   $69.85   $69.80  
  Purchase #4 $101.91   13.713%   $115.8849   $115.88   $115.90   $115.90  
  Purchase #5 $14.58   7.859%   $15.7258   $15.73   $15.75   $15.70  
  Purchase #6 $130.28   5.833%   $137.8792   $137.88   $137.90   $137.90  
  Purchase #7 $153.27   5.556%   $161.7857   $161.79   $161.80   $161.80  
  7 purchase totals = $643.51       $693.2070   $693.22   $693.30   $693.20