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 $202.81   8.274%   $219.5905   $219.59   $219.60   $219.60  
  Purchase #2 $48.81   11.292%   $54.3216   $54.32   $54.30   $54.30  
  Purchase #3 $196.87   11.679%   $219.8624   $219.86   $219.85   $219.90  
  Purchase #4 $164.99   6.235%   $175.2771   $175.28   $175.30   $175.30  
  Purchase #5 $235.84   8.215%   $255.2143   $255.21   $255.20   $255.20  
  Purchase #6 $111.41   13.202%   $126.1183   $126.12   $126.10   $126.10  
  Purchase #7 $211.66   3.812%   $219.7285   $219.73   $219.75   $219.70  
  7 purchase totals = $1,172.39       $1,270.1127   $1,270.11   $1,270.10   $1,270.10