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	$82.78	8.290%	$89.6425	$89.64	$89.65	$89.60
Purchase #2	$152.65	5.831%	$161.551	$161.55	$161.55	$161.60
Purchase #3	$179.63	8.645%	$195.159	$195.16	$195.15	$195.20
Purchase #4	$48.31	4.371%	$50.4216	$50.42	$50.40	$50.40
Purchase #5	$120.74	13.599%	$137.1594	$137.16	$137.15	$137.20
Purchase #6	$239.76	11.257%	$266.7498	$266.75	$266.75	$266.70
Purchase #7	$168.95	9.843%	$185.5797	$185.58	$185.60	$185.60
7 purchase totals =	$992.82		$1,086.2630	$1,086.26	$1,086.25	$1,086.30