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	$170.84	5.631%	$180.46	$180.46	$180.45	$180.50
Purchase #2	$103.39	10.524%	$114.2708	$114.27	$114.25	$114.30
Purchase #3	$38.64	13.322%	$43.7876	$43.79	$43.80	$43.80
Purchase #4	$136.34	11.281%	$151.7205	$151.72	$151.70	$151.70
Purchase #5	$207.30	7.734%	$223.3326	$223.33	$223.35	$223.30
Purchase #6	$90.69	11.306%	$100.9434	$100.94	$100.95	$100.90
Purchase #7	$32.44	11.704%	$36.2368	$36.24	$36.25	$36.20
7 purchase totals =	$779.64		$850.7517	$850.75	$850.75	$850.70