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	$129.78	5.396%	$136.7829	$136.78	$136.80	$136.80
Purchase #2	$160.33	5.858%	$169.7221	$169.72	$169.70	$169.70
Purchase #3	$90.78	11.815%	$101.5057	$101.51	$101.50	$101.50
Purchase #4	$150.72	11.244%	$167.667	$167.67	$167.65	$167.70
Purchase #5	$220.34	7.746%	$237.4075	$237.41	$237.40	$237.40
Purchase #6	$141.80	3.391%	$146.6084	$146.61	$146.60	$146.60
Purchase #7	$52.37	11.134%	$58.2009	$58.20	$58.20	$58.20
7 purchase totals =	$946.12		$1,017.8945	$1,017.90	$1,017.85	$1,017.90