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	$87.92	3.132%	$90.6737	$90.67	$90.65	$90.70
Purchase #2	$30.30	4.856%	$31.7714	$31.77	$31.75	$31.80
Purchase #3	$188.64	11.431%	$210.2034	$210.20	$210.20	$210.20
Purchase #4	$80.87	10.123%	$89.0565	$89.06	$89.05	$89.10
Purchase #5	$28.27	6.693%	$30.1621	$30.16	$30.15	$30.20
Purchase #6	$59.96	11.872%	$67.0785	$67.08	$67.10	$67.10
Purchase #7	$19.85	10.581%	$21.9503	$21.95	$21.95	$22.00
7 purchase totals =	$495.81		$540.8959	$540.89	$540.85	$541.10