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 $184.26   13.405%   $208.9601   $208.96   $208.95   $209.00  
  Purchase #2 $126.97   3.653%   $131.6082   $131.61   $131.60   $131.60  
  Purchase #3 $161.86   8.653%   $175.8657   $175.87   $175.85   $175.90  
  Purchase #4 $169.90   5.188%   $178.7144   $178.71   $178.70   $178.70  
  Purchase #5 $160.77   3.873%   $166.9966   $167.00   $167.00   $167.00  
  Purchase #6 $221.73   6.704%   $236.5948   $236.59   $236.60   $236.60  
  Purchase #7 $51.53   3.610%   $53.3902   $53.39   $53.40   $53.40  
  7 purchase totals = $1,077.02       $1,152.1300   $1,152.13   $1,152.10   $1,152.20