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 $58.76   12.754%   $66.2543   $66.25   $66.25   $66.30  
  Purchase #2 $163.87   8.493%   $177.7875   $177.79   $177.80   $177.80  
  Purchase #3 $223.47   13.457%   $253.5424   $253.54   $253.55   $253.50  
  Purchase #4 $244.63   9.346%   $267.4931   $267.49   $267.50   $267.50  
  Purchase #5 $68.67   13.161%   $77.7077   $77.71   $77.70   $77.70  
  Purchase #6 $192.62   11.785%   $215.3203   $215.32   $215.30   $215.30  
  Purchase #7 $18.62   3.731%   $19.3147   $19.31   $19.30   $19.30  
  7 purchase totals = $970.64       $1,077.4200   $1,077.41   $1,077.40   $1,077.40