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	$48.72	4.596%	$50.9592	$50.96	$50.95	$51.00
Purchase #2	$73.50	11.784%	$82.1612	$82.16	$82.15	$82.20
Purchase #3	$6.47	12.441%	$7.2749	$7.27	$7.25	$7.30
Purchase #4	$104.54	8.404%	$113.3255	$113.33	$113.35	$113.30
Purchase #5	$238.67	10.495%	$263.7184	$263.72	$263.70	$263.70
Purchase #6	$185.59	6.398%	$197.464	$197.46	$197.45	$197.50
Purchase #7	$52.71	5.874%	$55.8062	$55.81	$55.80	$55.80
7 purchase totals =	$710.20		$770.7094	$770.71	$770.65	$770.80