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 $224.97   12.476%   $253.0373   $253.04   $253.05   $253.00  
  Purchase #2 $144.32   3.139%   $148.8502   $148.85   $148.85   $148.90  
  Purchase #3 $172.36   11.795%   $192.6899   $192.69   $192.70   $192.70  
  Purchase #4 $216.49   6.712%   $231.0208   $231.02   $231.00   $231.00  
  Purchase #5 $242.49   10.460%   $267.8545   $267.85   $267.85   $267.90  
  Purchase #6 $185.35   5.817%   $196.1318   $196.13   $196.15   $196.10  
  Purchase #7 $157.74   13.289%   $178.7021   $178.70   $178.70   $178.70  
  7 purchase totals = $1,343.72       $1,468.2866   $1,468.28   $1,468.30   $1,468.30