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	$218.35	12.330%	$245.2726	$245.27	$245.25	$245.30
Purchase #2	$139.36	13.286%	$157.8754	$157.88	$157.90	$157.90
Purchase #3	$15.72	10.118%	$17.3105	$17.31	$17.30	$17.30
Purchase #4	$52.44	4.735%	$54.923	$54.92	$54.90	$54.90
Purchase #5	$73.25	7.751%	$78.9276	$78.93	$78.95	$78.90
Purchase #6	$140.58	3.755%	$145.8588	$145.86	$145.85	$145.90
Purchase #7	$146.70	9.524%	$160.6717	$160.67	$160.65	$160.70
7 purchase totals =	$786.40		$860.8396	$860.84	$860.80	$860.90