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	$109.30	7.465%	$117.4592	$117.46	$117.45	$117.50
Purchase #2	$179.96	6.242%	$191.1931	$191.19	$191.20	$191.20
Purchase #3	$156.34	6.619%	$166.6881	$166.69	$166.70	$166.70
Purchase #4	$145.27	4.482%	$151.781	$151.78	$151.80	$151.80
Purchase #5	$161.47	7.820%	$174.097	$174.10	$174.10	$174.10
Purchase #6	$91.86	5.194%	$96.6312	$96.63	$96.65	$96.60
Purchase #7	$55.32	5.750%	$58.5009	$58.50	$58.50	$58.50
7 purchase totals =	$899.52		$956.3505	$956.35	$956.40	$956.40