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	$121.69	5.625%	$128.5351	$128.54	$128.55	$128.50
Purchase #2	$151.55	10.202%	$167.0111	$167.01	$167.00	$167.00
Purchase #3	$72.68	11.835%	$81.2817	$81.28	$81.30	$81.30
Purchase #4	$220.58	11.442%	$245.8188	$245.82	$245.80	$245.80
Purchase #5	$72.83	10.140%	$80.215	$80.22	$80.20	$80.20
Purchase #6	$118.50	7.428%	$127.3022	$127.30	$127.30	$127.30
Purchase #7	$71.51	11.579%	$79.7901	$79.79	$79.80	$79.80
7 purchase totals =	$829.34		$909.9540	$909.96	$909.95	$909.90