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	$70.35	13.592%	$79.912	$79.91	$79.90	$79.90
Purchase #2	$83.38	7.111%	$89.3092	$89.31	$89.30	$89.30
Purchase #3	$24.36	6.664%	$25.9834	$25.98	$26.00	$26.00
Purchase #4	$17.88	4.657%	$18.7127	$18.71	$18.70	$18.70
Purchase #5	$57.64	7.424%	$61.9192	$61.92	$61.90	$61.90
Purchase #6	$149.45	10.297%	$164.8389	$164.84	$164.85	$164.80
Purchase #7	$87.87	13.229%	$99.4943	$99.49	$99.50	$99.50
7 purchase totals =	$490.93		$540.1697	$540.16	$540.15	$540.10