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	$79.74	11.850%	$89.1892	$89.19	$89.20	$89.20
Purchase #2	$164.85	8.584%	$179.0007	$179.00	$179.00	$179.00
Purchase #3	$89.48	11.191%	$99.4937	$99.49	$99.50	$99.50
Purchase #4	$127.29	8.332%	$137.8958	$137.90	$137.90	$137.90
Purchase #5	$67.82	4.678%	$70.9926	$70.99	$71.00	$71.00
Purchase #6	$237.65	9.700%	$260.7021	$260.70	$260.70	$260.70
Purchase #7	$114.37	11.217%	$127.1989	$127.20	$127.20	$127.20
7 purchase totals =	$881.20		$964.4730	$964.47	$964.50	$964.50