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	$19.61	5.132%	$20.6164	$20.62	$20.60	$20.60
Purchase #2	$196.35	9.840%	$215.6708	$215.67	$215.65	$215.70
Purchase #3	$176.57	7.502%	$189.8163	$189.82	$189.80	$189.80
Purchase #4	$206.49	4.466%	$215.7118	$215.71	$215.70	$215.70
Purchase #5	$105.46	5.802%	$111.5788	$111.58	$111.60	$111.60
Purchase #6	$206.66	3.237%	$213.3496	$213.35	$213.35	$213.30
Purchase #7	$111.56	12.523%	$125.5307	$125.53	$125.55	$125.50
7 purchase totals =	$1,022.70		$1,092.2744	$1,092.28	$1,092.25	$1,092.20