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	$243.28	12.677%	$274.1206	$274.12	$274.10	$274.10
Purchase #2	$93.75	7.562%	$100.8394	$100.84	$100.85	$100.80
Purchase #3	$161.77	6.232%	$171.8515	$171.85	$171.85	$171.90
Purchase #4	$50.55	13.346%	$57.2964	$57.30	$57.30	$57.30
Purchase #5	$222.72	5.647%	$235.297	$235.30	$235.30	$235.30
Purchase #6	$188.86	5.678%	$199.5835	$199.58	$199.60	$199.60
Purchase #7	$80.98	11.729%	$90.4781	$90.48	$90.50	$90.50
7 purchase totals =	$1,041.91		$1,129.4665	$1,129.47	$1,129.50	$1,129.50