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 $190.45   8.516%   $206.6687   $206.67   $206.65   $206.70  
  Purchase #2 $242.56   3.441%   $250.9065   $250.91   $250.90   $250.90  
  Purchase #3 $52.60   4.256%   $54.8387   $54.84   $54.85   $54.80  
  Purchase #4 $157.92   3.282%   $163.1029   $163.10   $163.10   $163.10  
  Purchase #5 $134.64   6.607%   $143.5357   $143.54   $143.55   $143.50  
  Purchase #6 $163.30   10.628%   $180.6555   $180.66   $180.65   $180.70  
  Purchase #7 $51.92   6.873%   $55.4885   $55.49   $55.50   $55.50  
  7 purchase totals = $993.39       $1,055.1965   $1,055.21   $1,055.20   $1,055.20