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	$11.84	3.712%	$12.2795	$12.28	$12.30	$12.30
Purchase #2	$247.76	7.616%	$266.6294	$266.63	$266.65	$266.60
Purchase #3	$79.74	3.176%	$82.2725	$82.27	$82.25	$82.30
Purchase #4	$240.90	9.363%	$263.4555	$263.46	$263.45	$263.50
Purchase #5	$140.90	10.350%	$155.4832	$155.48	$155.50	$155.50
Purchase #6	$175.74	9.189%	$191.8887	$191.89	$191.90	$191.90
Purchase #7	$30.38	4.232%	$31.6657	$31.67	$31.65	$31.70
7 purchase totals =	$927.26		$1,003.6745	$1,003.68	$1,003.70	$1,003.80