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	$90.91	9.383%	$99.4401	$99.44	$99.45	$99.40
Purchase #2	$90.67	9.344%	$99.1422	$99.14	$99.15	$99.10
Purchase #3	$210.62	3.180%	$217.3177	$217.32	$217.30	$217.30
Purchase #4	$43.78	8.402%	$47.4584	$47.46	$47.45	$47.50
Purchase #5	$105.76	7.356%	$113.5397	$113.54	$113.55	$113.50
Purchase #6	$22.50	13.237%	$25.4783	$25.48	$25.50	$25.50
Purchase #7	$78.42	3.366%	$81.0596	$81.06	$81.05	$81.10
7 purchase totals =	$642.66		$683.4360	$683.44	$683.45	$683.40