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 $60.33   6.379%   $64.1785   $64.18   $64.20   $64.20  
  Purchase #2 $164.55   8.668%   $178.8132   $178.81   $178.80   $178.80  
  Purchase #3 $231.85   4.629%   $242.5823   $242.58   $242.60   $242.60  
  Purchase #4 $25.33   9.698%   $27.7865   $27.79   $27.80   $27.80  
  Purchase #5 $42.44   5.670%   $44.8463   $44.85   $44.85   $44.80  
  Purchase #6 $240.71   5.558%   $254.0887   $254.09   $254.10   $254.10  
  Purchase #7 $180.80   6.695%   $192.9046   $192.90   $192.90   $192.90  
  7 purchase totals = $946.01       $1,005.2001   $1,005.20   $1,005.25   $1,005.20