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	$250.38	13.745%	$284.7947	$284.79	$284.80	$284.80
Purchase #2	$201.87	13.792%	$229.7119	$229.71	$229.70	$229.70
Purchase #3	$39.62	6.695%	$42.2726	$42.27	$42.25	$42.30
Purchase #4	$140.94	6.820%	$150.5521	$150.55	$150.55	$150.60
Purchase #5	$108.60	5.371%	$114.4329	$114.43	$114.45	$114.40
Purchase #6	$240.60	10.851%	$266.7075	$266.71	$266.70	$266.70
Purchase #7	$216.29	13.406%	$245.2858	$245.29	$245.30	$245.30
7 purchase totals =	$1,198.30		$1,333.7575	$1,333.75	$1,333.75	$1,333.80