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 $156.69   7.624%   $168.636   $168.64   $168.65   $168.60  
  Purchase #2 $234.95   10.167%   $258.8374   $258.84   $258.85   $258.80  
  Purchase #3 $214.47   4.596%   $224.327   $224.33   $224.35   $224.30  
  Purchase #4 $164.85   13.347%   $186.8525   $186.85   $186.85   $186.90  
  Purchase #5 $205.80   9.706%   $225.7749   $225.77   $225.75   $225.80  
  Purchase #6 $228.87   11.695%   $255.6363   $255.64   $255.65   $255.60  
  Purchase #7 $126.34   10.525%   $139.6373   $139.64   $139.65   $139.60  
  7 purchase totals = $1,331.97       $1,459.7014   $1,459.71   $1,459.75   $1,459.60