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	$77.85	11.809%	$87.0433	$87.04	$87.05	$87.00
Purchase #2	$96.86	5.438%	$102.1272	$102.13	$102.15	$102.10
Purchase #3	$113.61	8.558%	$123.3327	$123.33	$123.35	$123.30
Purchase #4	$188.79	4.793%	$197.8387	$197.84	$197.85	$197.80
Purchase #5	$48.54	3.616%	$50.2952	$50.30	$50.30	$50.30
Purchase #6	$78.56	5.776%	$83.0976	$83.10	$83.10	$83.10
Purchase #7	$143.56	10.412%	$158.5075	$158.51	$158.50	$158.50
7 purchase totals =	$747.77		$802.2422	$802.25	$802.30	$802.10