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	$105.50	11.354%	$117.4785	$117.48	$117.50	$117.50
Purchase #2	$40.91	6.781%	$43.6841	$43.68	$43.70	$43.70
Purchase #3	$146.52	13.362%	$166.098	$166.10	$166.10	$166.10
Purchase #4	$29.86	11.732%	$33.3632	$33.36	$33.35	$33.40
Purchase #5	$150.46	6.404%	$160.0955	$160.10	$160.10	$160.10
Purchase #6	$111.40	3.669%	$115.4873	$115.49	$115.50	$115.50
Purchase #7	$144.75	3.735%	$150.1564	$150.16	$150.15	$150.20
7 purchase totals =	$729.40		$786.3630	$786.37	$786.40	$786.50