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	$37.76	13.809%	$42.9743	$42.97	$42.95	$43.00
Purchase #2	$243.59	8.608%	$264.5582	$264.56	$264.55	$264.60
Purchase #3	$52.89	5.740%	$55.9259	$55.93	$55.95	$55.90
Purchase #4	$86.63	4.126%	$90.2044	$90.20	$90.20	$90.20
Purchase #5	$243.49	13.109%	$275.4091	$275.41	$275.40	$275.40
Purchase #6	$37.87	8.461%	$41.0742	$41.07	$41.05	$41.10
Purchase #7	$116.90	11.798%	$130.6919	$130.69	$130.70	$130.70
7 purchase totals =	$819.13		$900.8380	$900.83	$900.80	$900.90