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	$19.56	4.714%	$20.4821	$20.48	$20.50	$20.50
Purchase #2	$52.74	12.446%	$59.304	$59.30	$59.30	$59.30
Purchase #3	$138.36	5.465%	$145.9214	$145.92	$145.90	$145.90
Purchase #4	$115.57	11.262%	$128.5855	$128.59	$128.60	$128.60
Purchase #5	$79.32	8.335%	$85.9313	$85.93	$85.95	$85.90
Purchase #6	$15.43	5.702%	$16.3098	$16.31	$16.30	$16.30
Purchase #7	$86.60	11.258%	$96.3494	$96.35	$96.35	$96.30
7 purchase totals =	$507.58		$552.8835	$552.88	$552.90	$552.80