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	$134.41	6.312%	$142.894	$142.89	$142.90	$142.90
Purchase #2	$123.37	13.145%	$139.587	$139.59	$139.60	$139.60
Purchase #3	$153.78	12.466%	$172.9502	$172.95	$172.95	$173.00
Purchase #4	$52.45	10.551%	$57.984	$57.98	$58.00	$58.00
Purchase #5	$97.81	11.467%	$109.0259	$109.03	$109.05	$109.00
Purchase #6	$181.96	8.276%	$197.019	$197.02	$197.00	$197.00
Purchase #7	$91.46	13.305%	$103.6288	$103.63	$103.65	$103.60
7 purchase totals =	$835.24		$923.0889	$923.09	$923.15	$923.10