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	$79.76	10.611%	$88.2233	$88.22	$88.20	$88.20
Purchase #2	$96.72	3.182%	$99.7976	$99.80	$99.80	$99.80
Purchase #3	$120.82	5.445%	$127.3986	$127.40	$127.40	$127.40
Purchase #4	$227.93	9.827%	$250.3287	$250.33	$250.35	$250.30
Purchase #5	$63.58	11.782%	$71.071	$71.07	$71.05	$71.10
Purchase #6	$131.96	3.452%	$136.5153	$136.52	$136.50	$136.50
Purchase #7	$152.82	8.663%	$166.0588	$166.06	$166.05	$166.10
7 purchase totals =	$873.59		$939.3933	$939.40	$939.35	$939.40