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 $111.93   5.862%   $118.4913   $118.49   $118.50   $118.50  
  Purchase #2 $92.91   4.110%   $96.7286   $96.73   $96.75   $96.70  
  Purchase #3 $236.80   4.172%   $246.6793   $246.68   $246.70   $246.70  
  Purchase #4 $170.69   10.247%   $188.1806   $188.18   $188.20   $188.20  
  Purchase #5 $8.74   13.797%   $9.9459   $9.95   $9.95   $9.90  
  Purchase #6 $178.49   6.831%   $190.6827   $190.68   $190.70   $190.70  
  Purchase #7 $246.72   10.719%   $273.1659   $273.17   $273.15   $273.20  
  7 purchase totals = $1,046.28       $1,123.8743   $1,123.88   $1,123.95   $1,123.90