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	$88.58	12.586%	$99.7287	$99.73	$99.75	$99.70
Purchase #2	$158.41	12.719%	$178.5582	$178.56	$178.55	$178.60
Purchase #3	$58.32	4.415%	$60.8948	$60.89	$60.90	$60.90
Purchase #4	$19.40	10.832%	$21.5014	$21.50	$21.50	$21.50
Purchase #5	$93.72	11.670%	$104.6571	$104.66	$104.65	$104.70
Purchase #6	$212.37	7.813%	$228.9625	$228.96	$228.95	$229.00
Purchase #7	$39.94	6.211%	$42.4207	$42.42	$42.40	$42.40
7 purchase totals =	$670.74		$736.7234	$736.72	$736.70	$736.80