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 $212.93   13.677%   $242.0524   $242.05   $242.05   $242.10  
  Purchase #2 $147.53   11.197%   $164.0489   $164.05   $164.05   $164.00  
  Purchase #3 $91.87   6.201%   $97.5669   $97.57   $97.55   $97.60  
  Purchase #4 $194.75   3.286%   $201.1495   $201.15   $201.15   $201.10  
  Purchase #5 $224.36   7.633%   $241.4854   $241.49   $241.50   $241.50  
  Purchase #6 $200.82   11.400%   $223.7135   $223.71   $223.70   $223.70  
  Purchase #7 $57.70   10.578%   $63.8035   $63.80   $63.80   $63.80  
  7 purchase totals = $1,129.96       $1,233.8201   $1,233.82   $1,233.80   $1,233.80