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	$137.51	12.703%	$154.9779	$154.98	$155.00	$155.00
Purchase #2	$111.74	5.526%	$117.9148	$117.91	$117.90	$117.90
Purchase #3	$50.39	13.635%	$57.2607	$57.26	$57.25	$57.30
Purchase #4	$35.46	6.511%	$37.7688	$37.77	$37.75	$37.80
Purchase #5	$30.46	3.787%	$31.6135	$31.61	$31.60	$31.60
Purchase #6	$138.80	5.409%	$146.3077	$146.31	$146.30	$146.30
Purchase #7	$223.65	3.513%	$231.5068	$231.51	$231.50	$231.50
7 purchase totals =	$728.01		$777.3502	$777.35	$777.30	$777.40