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	$35.92	10.869%	$39.8241	$39.82	$39.80	$39.80
Purchase #2	$58.70	13.190%	$66.4425	$66.44	$66.45	$66.40
Purchase #3	$165.74	5.316%	$174.5507	$174.55	$174.55	$174.60
Purchase #4	$86.30	4.605%	$90.2741	$90.27	$90.25	$90.30
Purchase #5	$162.39	5.187%	$170.8132	$170.81	$170.80	$170.80
Purchase #6	$81.86	8.281%	$88.6388	$88.64	$88.65	$88.60
Purchase #7	$74.36	5.367%	$78.3509	$78.35	$78.35	$78.40
7 purchase totals =	$665.27		$708.8943	$708.88	$708.85	$708.90