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	$77.76	6.618%	$82.9062	$82.91	$82.90	$82.90
Purchase #2	$129.90	12.466%	$146.0933	$146.09	$146.10	$146.10
Purchase #3	$29.66	6.770%	$31.668	$31.67	$31.65	$31.70
Purchase #4	$189.71	11.809%	$212.1129	$212.11	$212.10	$212.10
Purchase #5	$99.52	9.633%	$109.1068	$109.11	$109.10	$109.10
Purchase #6	$206.84	11.352%	$230.3205	$230.32	$230.30	$230.30
Purchase #7	$20.49	4.368%	$21.385	$21.39	$21.40	$21.40
7 purchase totals =	$753.88		$833.5927	$833.60	$833.55	$833.60