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	$6.38	9.652%	$6.9958	$7.00	$7.00	$7.00
Purchase #2	$156.76	6.788%	$167.4009	$167.40	$167.40	$167.40
Purchase #3	$63.46	11.553%	$70.7915	$70.79	$70.80	$70.80
Purchase #4	$150.52	10.648%	$166.5474	$166.55	$166.55	$166.50
Purchase #5	$42.48	6.867%	$45.3971	$45.40	$45.40	$45.40
Purchase #6	$46.71	7.763%	$50.3361	$50.34	$50.35	$50.30
Purchase #7	$86.35	5.564%	$91.1545	$91.15	$91.15	$91.20
7 purchase totals =	$552.66		$598.6233	$598.63	$598.65	$598.60