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	$143.34	9.277%	$156.6377	$156.64	$156.65	$156.60
Purchase #2	$222.57	12.272%	$249.8838	$249.88	$249.90	$249.90
Purchase #3	$224.37	4.133%	$233.6432	$233.64	$233.65	$233.60
Purchase #4	$199.54	10.621%	$220.7331	$220.73	$220.75	$220.70
Purchase #5	$133.91	5.152%	$140.809	$140.81	$140.80	$140.80
Purchase #6	$136.42	4.370%	$142.3816	$142.38	$142.40	$142.40
Purchase #7	$118.49	10.661%	$131.1222	$131.12	$131.10	$131.10
7 purchase totals =	$1,178.64		$1,275.2106	$1,275.20	$1,275.25	$1,275.10