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	$181.58	10.322%	$200.3227	$200.32	$200.30	$200.30
Purchase #2	$67.74	4.231%	$70.6061	$70.61	$70.60	$70.60
Purchase #3	$120.93	9.282%	$132.1547	$132.15	$132.15	$132.20
Purchase #4	$107.98	4.236%	$112.554	$112.55	$112.55	$112.60
Purchase #5	$20.89	7.135%	$22.3805	$22.38	$22.40	$22.40
Purchase #6	$49.69	5.791%	$52.5675	$52.57	$52.55	$52.60
Purchase #7	$71.48	8.219%	$77.3549	$77.35	$77.35	$77.40
7 purchase totals =	$620.29		$667.9404	$667.93	$667.90	$668.10