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 $238.41   11.866%   $266.6997   $266.70   $266.70   $266.70  
  Purchase #2 $35.53   4.568%   $37.153   $37.15   $37.15   $37.20  
  Purchase #3 $47.39   3.595%   $49.0937   $49.09   $49.10   $49.10  
  Purchase #4 $234.33   4.847%   $245.688   $245.69   $245.70   $245.70  
  Purchase #5 $246.42   12.807%   $277.979   $277.98   $278.00   $278.00  
  Purchase #6 $175.70   12.355%   $197.4077   $197.41   $197.40   $197.40  
  Purchase #7 $13.70   10.776%   $15.1763   $15.18   $15.20   $15.20  
  7 purchase totals = $991.48       $1,089.1974   $1,089.20   $1,089.25   $1,089.30