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	$160.47	6.289%	$170.562	$170.56	$170.55	$170.60
Purchase #2	$158.84	13.638%	$180.5026	$180.50	$180.50	$180.50
Purchase #3	$132.77	3.411%	$137.2988	$137.30	$137.30	$137.30
Purchase #4	$54.88	8.287%	$59.4279	$59.43	$59.45	$59.40
Purchase #5	$142.75	6.377%	$151.8532	$151.85	$151.85	$151.90
Purchase #6	$57.46	5.687%	$60.7278	$60.73	$60.75	$60.70
Purchase #7	$101.81	7.182%	$109.122	$109.12	$109.10	$109.10
7 purchase totals =	$808.98		$869.4943	$869.49	$869.50	$869.50