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 $227.97   10.674%   $252.3035   $252.30   $252.30   $252.30  
  Purchase #2 $61.83   3.384%   $63.9223   $63.92   $63.90   $63.90  
  Purchase #3 $240.92   8.114%   $260.4682   $260.47   $260.45   $260.50  
  Purchase #4 $211.30   5.798%   $223.5512   $223.55   $223.55   $223.60  
  Purchase #5 $205.70   8.240%   $222.6497   $222.65   $222.65   $222.60  
  Purchase #6 $42.63   8.327%   $46.1798   $46.18   $46.20   $46.20  
  Purchase #7 $139.32   6.114%   $147.838   $147.84   $147.85   $147.80  
  7 purchase totals = $1,129.67       $1,216.9127   $1,216.91   $1,216.90   $1,216.90