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	$30.87	7.807%	$33.28	$33.28	$33.30	$33.30
Purchase #2	$107.88	10.149%	$118.8287	$118.83	$118.85	$118.80
Purchase #3	$247.75	9.729%	$271.8536	$271.85	$271.85	$271.90
Purchase #4	$64.87	10.684%	$71.8007	$71.80	$71.80	$71.80
Purchase #5	$185.81	12.816%	$209.6234	$209.62	$209.60	$209.60
Purchase #6	$144.77	8.164%	$156.589	$156.59	$156.60	$156.60
Purchase #7	$74.34	7.760%	$80.1088	$80.11	$80.10	$80.10
7 purchase totals =	$856.29		$942.0842	$942.08	$942.10	$942.10