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	$147.93	12.256%	$166.0603	$166.06	$166.05	$166.10
Purchase #2	$136.56	3.172%	$140.8917	$140.89	$140.90	$140.90
Purchase #3	$133.97	13.403%	$151.926	$151.93	$151.95	$151.90
Purchase #4	$165.50	12.106%	$185.5354	$185.54	$185.55	$185.50
Purchase #5	$90.66	3.323%	$93.6726	$93.67	$93.65	$93.70
Purchase #6	$69.54	11.555%	$77.5753	$77.58	$77.60	$77.60
Purchase #7	$58.88	3.711%	$61.065	$61.07	$61.05	$61.10
7 purchase totals =	$803.04		$876.7263	$876.74	$876.75	$876.80