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	$108.51	13.711%	$123.3878	$123.39	$123.40	$123.40
Purchase #2	$7.82	3.870%	$8.1226	$8.12	$8.10	$8.10
Purchase #3	$137.68	6.278%	$146.3236	$146.32	$146.30	$146.30
Purchase #4	$149.59	11.323%	$166.5281	$166.53	$166.55	$166.50
Purchase #5	$61.48	3.787%	$63.8082	$63.81	$63.80	$63.80
Purchase #6	$101.48	13.600%	$115.2813	$115.28	$115.30	$115.30
Purchase #7	$54.98	13.596%	$62.4551	$62.46	$62.45	$62.50
7 purchase totals =	$621.54		$685.9067	$685.91	$685.90	$685.90