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 $115.83   8.620%   $125.8145   $125.81   $125.80   $125.80  
  Purchase #2 $90.39   8.496%   $98.0695   $98.07   $98.05   $98.10  
  Purchase #3 $233.61   9.862%   $256.6486   $256.65   $256.65   $256.60  
  Purchase #4 $246.72   5.662%   $260.6893   $260.69   $260.70   $260.70  
  Purchase #5 $115.81   6.401%   $123.223   $123.22   $123.20   $123.20  
  Purchase #6 $196.26   6.245%   $208.5164   $208.52   $208.50   $208.50  
  Purchase #7 $179.93   9.656%   $197.304   $197.30   $197.30   $197.30  
  7 purchase totals = $1,178.55       $1,270.2653   $1,270.26   $1,270.20   $1,270.20