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	$54.31	10.375%	$59.9447	$59.94	$59.95	$59.90
Purchase #2	$105.70	11.242%	$117.5828	$117.58	$117.60	$117.60
Purchase #3	$19.34	3.848%	$20.0842	$20.08	$20.10	$20.10
Purchase #4	$201.87	13.715%	$229.5565	$229.56	$229.55	$229.60
Purchase #5	$69.89	11.831%	$78.1587	$78.16	$78.15	$78.20
Purchase #6	$71.45	10.126%	$78.685	$78.69	$78.70	$78.70
Purchase #7	$62.77	13.809%	$71.4379	$71.44	$71.45	$71.40
7 purchase totals =	$585.33		$655.4498	$655.45	$655.50	$655.50