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	$40.29	6.421%	$42.877	$42.88	$42.90	$42.90
Purchase #2	$26.30	10.756%	$29.1288	$29.13	$29.15	$29.10
Purchase #3	$18.62	6.734%	$19.8739	$19.87	$19.85	$19.90
Purchase #4	$189.92	3.282%	$196.1532	$196.15	$196.15	$196.20
Purchase #5	$235.61	5.492%	$248.5497	$248.55	$248.55	$248.50
Purchase #6	$28.79	13.693%	$32.7322	$32.73	$32.75	$32.70
Purchase #7	$250.32	3.467%	$258.9986	$259.00	$259.00	$259.00
7 purchase totals =	$789.85		$828.3134	$828.31	$828.35	$828.30