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	$139.32	4.281%	$145.2843	$145.28	$145.30	$145.30
Purchase #2	$100.53	8.566%	$109.1414	$109.14	$109.15	$109.10
Purchase #3	$220.62	3.497%	$228.3351	$228.34	$228.35	$228.30
Purchase #4	$85.66	7.861%	$92.3937	$92.39	$92.40	$92.40
Purchase #5	$143.28	6.635%	$152.7866	$152.79	$152.80	$152.80
Purchase #6	$76.59	9.510%	$83.8737	$83.87	$83.85	$83.90
Purchase #7	$72.90	5.521%	$76.9248	$76.92	$76.90	$76.90
7 purchase totals =	$838.90		$888.7396	$888.73	$888.75	$888.70