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	$84.26	5.576%	$88.9583	$88.96	$88.95	$89.00
Purchase #2	$63.86	6.142%	$67.7823	$67.78	$67.80	$67.80
Purchase #3	$11.76	11.585%	$13.1224	$13.12	$13.10	$13.10
Purchase #4	$213.35	8.674%	$231.856	$231.86	$231.85	$231.90
Purchase #5	$203.90	13.712%	$231.8588	$231.86	$231.85	$231.90
Purchase #6	$172.89	10.600%	$191.2163	$191.22	$191.20	$191.20
Purchase #7	$60.25	3.485%	$62.3497	$62.35	$62.35	$62.30
7 purchase totals =	$810.27		$887.1438	$887.15	$887.10	$887.20