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	$90.27	4.476%	$94.3105	$94.31	$94.30	$94.30
Purchase #2	$209.71	12.278%	$235.4582	$235.46	$235.45	$235.50
Purchase #3	$51.57	4.534%	$53.9082	$53.91	$53.90	$53.90
Purchase #4	$182.38	6.409%	$194.0687	$194.07	$194.05	$194.10
Purchase #5	$35.25	6.257%	$37.4556	$37.46	$37.45	$37.50
Purchase #6	$170.87	12.327%	$191.9331	$191.93	$191.95	$191.90
Purchase #7	$49.93	12.480%	$56.1613	$56.16	$56.15	$56.20
7 purchase totals =	$789.98		$863.2956	$863.30	$863.25	$863.40