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 $211.56   4.719%   $221.5435   $221.54   $221.55   $221.50  
  Purchase #2 $103.41   4.156%   $107.7077   $107.71   $107.70   $107.70  
  Purchase #3 $164.45   6.291%   $174.7955   $174.80   $174.80   $174.80  
  Purchase #4 $119.33   5.830%   $126.2869   $126.29   $126.30   $126.30  
  Purchase #5 $28.91   5.749%   $30.572   $30.57   $30.55   $30.60  
  Purchase #6 $148.57   12.281%   $166.8159   $166.82   $166.80   $166.80  
  Purchase #7 $250.47   10.477%   $276.7117   $276.71   $276.70   $276.70  
  7 purchase totals = $1,026.70       $1,104.4332   $1,104.44   $1,104.40   $1,104.40