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 $249.46   4.572%   $260.8653   $260.87   $260.85   $260.90  
  Purchase #2 $228.66   8.726%   $248.6129   $248.61   $248.60   $248.60  
  Purchase #3 $118.42   6.351%   $125.9409   $125.94   $125.95   $125.90  
  Purchase #4 $158.82   11.127%   $176.4919   $176.49   $176.50   $176.50  
  Purchase #5 $124.38   3.325%   $128.5156   $128.52   $128.50   $128.50  
  Purchase #6 $38.44   3.573%   $39.8135   $39.81   $39.80   $39.80  
  Purchase #7 $31.54   8.170%   $34.1168   $34.12   $34.10   $34.10  
  7 purchase totals = $949.72       $1,014.3569   $1,014.36   $1,014.30   $1,014.30