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	$75.79	9.674%	$83.1219	$83.12	$83.10	$83.10
Purchase #2	$243.92	12.842%	$275.2442	$275.24	$275.25	$275.20
Purchase #3	$72.87	8.203%	$78.8475	$78.85	$78.85	$78.80
Purchase #4	$82.57	11.853%	$92.357	$92.36	$92.35	$92.40
Purchase #5	$138.37	4.621%	$144.7641	$144.76	$144.75	$144.80
Purchase #6	$68.62	13.708%	$78.0264	$78.03	$78.05	$78.00
Purchase #7	$49.73	8.627%	$54.0202	$54.02	$54.00	$54.00
7 purchase totals =	$731.87		$806.3813	$806.38	$806.35	$806.30