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	$86.90	3.178%	$89.6617	$89.66	$89.65	$89.70
Purchase #2	$137.89	12.119%	$154.6009	$154.60	$154.60	$154.60
Purchase #3	$237.58	9.627%	$260.4518	$260.45	$260.45	$260.50
Purchase #4	$132.71	9.687%	$145.5656	$145.57	$145.55	$145.60
Purchase #5	$35.26	6.231%	$37.4571	$37.46	$37.45	$37.50
Purchase #6	$232.25	4.791%	$243.3771	$243.38	$243.40	$243.40
Purchase #7	$143.73	11.337%	$160.0247	$160.02	$160.00	$160.00
7 purchase totals =	$1,006.32		$1,091.1389	$1,091.14	$1,091.10	$1,091.30