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 $205.39   8.301%   $222.4394   $222.44   $222.45   $222.40  
  Purchase #2 $221.92   4.392%   $231.6667   $231.67   $231.65   $231.70  
  Purchase #3 $107.93   7.612%   $116.1456   $116.15   $116.15   $116.10  
  Purchase #4 $59.57   10.212%   $65.6533   $65.65   $65.65   $65.70  
  Purchase #5 $223.47   11.734%   $249.692   $249.69   $249.70   $249.70  
  Purchase #6 $218.66   12.745%   $246.5282   $246.53   $246.55   $246.50  
  Purchase #7 $79.53   4.813%   $83.3578   $83.36   $83.35   $83.40  
  7 purchase totals = $1,116.47       $1,215.4830   $1,215.49   $1,215.50   $1,215.50