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	$28.27	8.663%	$30.719	$30.72	$30.70	$30.70
Purchase #2	$240.43	10.839%	$266.4902	$266.49	$266.50	$266.50
Purchase #3	$7.93	6.145%	$8.4173	$8.42	$8.40	$8.40
Purchase #4	$216.89	9.862%	$238.2797	$238.28	$238.30	$238.30
Purchase #5	$227.62	11.230%	$253.1817	$253.18	$253.20	$253.20
Purchase #6	$172.34	7.489%	$185.2465	$185.25	$185.25	$185.20
Purchase #7	$77.66	6.801%	$82.9417	$82.94	$82.95	$82.90
7 purchase totals =	$971.14		$1,065.2761	$1,065.28	$1,065.30	$1,065.20