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	$143.63	3.607%	$148.8107	$148.81	$148.80	$148.80
Purchase #2	$120.46	6.502%	$128.2923	$128.29	$128.30	$128.30
Purchase #3	$87.95	13.674%	$99.9763	$99.98	$100.00	$100.00
Purchase #4	$54.40	6.299%	$57.8267	$57.83	$57.85	$57.80
Purchase #5	$14.77	10.285%	$16.2891	$16.29	$16.30	$16.30
Purchase #6	$37.93	7.803%	$40.8897	$40.89	$40.90	$40.90
Purchase #7	$110.58	9.297%	$120.8606	$120.86	$120.85	$120.90
7 purchase totals =	$569.72		$612.9454	$612.95	$613.00	$613.00