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 $76.93   10.446%   $84.9661   $84.97   $84.95   $85.00  
  Purchase #2 $98.71   5.109%   $103.7531   $103.75   $103.75   $103.80  
  Purchase #3 $32.59   6.742%   $34.7872   $34.79   $34.80   $34.80  
  Purchase #4 $72.40   4.777%   $75.8585   $75.86   $75.85   $75.90  
  Purchase #5 $86.93   9.861%   $95.5022   $95.50   $95.50   $95.50  
  Purchase #6 $53.32   8.423%   $57.8111   $57.81   $57.80   $57.80  
  Purchase #7 $99.49   3.753%   $103.2239   $103.22   $103.20   $103.20  
  7 purchase totals = $520.37       $555.9021   $555.90   $555.85   $556.00