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 $114.47   9.226%   $125.031   $125.03   $125.05   $125.00  
  Purchase #2 $26.71   7.506%   $28.7149   $28.71   $28.70   $28.70  
  Purchase #3 $90.54   10.575%   $100.1146   $100.11   $100.10   $100.10  
  Purchase #4 $13.79   6.106%   $14.632   $14.63   $14.65   $14.60  
  Purchase #5 $223.70   3.505%   $231.5407   $231.54   $231.55   $231.50  
  Purchase #6 $160.90   11.118%   $178.7889   $178.79   $178.80   $178.80  
  Purchase #7 $228.95   8.453%   $248.3031   $248.30   $248.30   $248.30  
  7 purchase totals = $859.06       $927.1252   $927.11   $927.15   $927.00