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	$84.78	3.579%	$87.8143	$87.81	$87.80	$87.80
Purchase #2	$19.91	3.663%	$20.6393	$20.64	$20.65	$20.60
Purchase #3	$92.49	8.425%	$100.2823	$100.28	$100.30	$100.30
Purchase #4	$75.44	10.107%	$83.0647	$83.06	$83.05	$83.10
Purchase #5	$191.40	10.167%	$210.8596	$210.86	$210.85	$210.90
Purchase #6	$33.86	5.613%	$35.7606	$35.76	$35.75	$35.80
Purchase #7	$117.96	10.847%	$130.7551	$130.76	$130.75	$130.80
7 purchase totals =	$615.84		$669.1759	$669.17	$669.15	$669.30