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	$167.94	12.295%	$188.5882	$188.59	$188.60	$188.60
Purchase #2	$128.86	9.748%	$141.4213	$141.42	$141.40	$141.40
Purchase #3	$162.82	10.705%	$180.2499	$180.25	$180.25	$180.20
Purchase #4	$90.42	3.445%	$93.535	$93.54	$93.55	$93.50
Purchase #5	$200.97	6.558%	$214.1496	$214.15	$214.15	$214.10
Purchase #6	$118.86	12.399%	$133.5975	$133.60	$133.60	$133.60
Purchase #7	$102.89	8.103%	$111.2272	$111.23	$111.25	$111.20
7 purchase totals =	$972.76		$1,062.7687	$1,062.78	$1,062.80	$1,062.60