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	$52.43	13.431%	$59.4719	$59.47	$59.45	$59.50
Purchase #2	$67.30	11.717%	$75.1855	$75.19	$75.20	$75.20
Purchase #3	$147.71	10.326%	$162.9625	$162.96	$162.95	$163.00
Purchase #4	$125.85	4.238%	$131.1835	$131.18	$131.20	$131.20
Purchase #5	$65.92	9.842%	$72.4078	$72.41	$72.40	$72.40
Purchase #6	$87.56	3.826%	$90.91	$90.91	$90.90	$90.90
Purchase #7	$60.38	4.321%	$62.989	$62.99	$63.00	$63.00
7 purchase totals =	$607.15		$655.1102	$655.11	$655.10	$655.20