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	$30.35	11.311%	$33.7829	$33.78	$33.80	$33.80
Purchase #2	$47.32	6.132%	$50.2217	$50.22	$50.20	$50.20
Purchase #3	$154.89	9.305%	$169.3025	$169.30	$169.30	$169.30
Purchase #4	$133.70	3.255%	$138.0519	$138.05	$138.05	$138.10
Purchase #5	$90.79	11.404%	$101.1437	$101.14	$101.15	$101.10
Purchase #6	$198.78	4.860%	$208.4407	$208.44	$208.45	$208.40
Purchase #7	$80.59	3.789%	$83.6436	$83.64	$83.65	$83.60
7 purchase totals =	$736.42		$784.5870	$784.57	$784.60	$784.50