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 $231.67   7.181%   $248.3062   $248.31   $248.30   $248.30  
  Purchase #2 $162.45   9.108%   $177.2459   $177.25   $177.25   $177.20  
  Purchase #3 $120.79   11.144%   $134.2508   $134.25   $134.25   $134.30  
  Purchase #4 $204.93   7.309%   $219.9083   $219.91   $219.90   $219.90  
  Purchase #5 $26.49   4.606%   $27.7101   $27.71   $27.70   $27.70  
  Purchase #6 $158.54   11.566%   $176.8767   $176.88   $176.90   $176.90  
  Purchase #7 $217.31   3.265%   $224.4052   $224.41   $224.40   $224.40  
  7 purchase totals = $1,122.18       $1,208.7032   $1,208.72   $1,208.70   $1,208.70