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	$103.80	6.206%	$110.2418	$110.24	$110.25	$110.20
Purchase #2	$158.95	7.790%	$171.3322	$171.33	$171.35	$171.30
Purchase #3	$204.46	6.796%	$218.3551	$218.36	$218.35	$218.40
Purchase #4	$139.72	13.236%	$158.2133	$158.21	$158.20	$158.20
Purchase #5	$100.40	4.849%	$105.2684	$105.27	$105.25	$105.30
Purchase #6	$131.75	5.705%	$139.2663	$139.27	$139.25	$139.30
Purchase #7	$16.62	9.599%	$18.2154	$18.22	$18.20	$18.20
7 purchase totals =	$855.70		$920.8925	$920.90	$920.85	$920.90