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	$24.91	13.140%	$28.1832	$28.18	$28.20	$28.20
Purchase #2	$50.56	11.721%	$56.4861	$56.49	$56.50	$56.50
Purchase #3	$171.42	6.346%	$182.2983	$182.30	$182.30	$182.30
Purchase #4	$37.69	3.256%	$38.9172	$38.92	$38.90	$38.90
Purchase #5	$113.55	6.407%	$120.8251	$120.83	$120.85	$120.80
Purchase #6	$32.71	3.695%	$33.9186	$33.92	$33.90	$33.90
Purchase #7	$215.72	13.435%	$244.702	$244.70	$244.70	$244.70
7 purchase totals =	$646.56		$705.3305	$705.34	$705.35	$705.30