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	$39.59	6.763%	$42.2675	$42.27	$42.25	$42.30
Purchase #2	$211.29	10.506%	$233.4881	$233.49	$233.50	$233.50
Purchase #3	$128.52	7.825%	$138.5767	$138.58	$138.60	$138.60
Purchase #4	$71.41	12.849%	$80.5855	$80.59	$80.60	$80.60
Purchase #5	$209.62	11.424%	$233.567	$233.57	$233.55	$233.60
Purchase #6	$130.45	13.461%	$148.0099	$148.01	$148.00	$148.00
Purchase #7	$124.91	6.724%	$133.3089	$133.31	$133.30	$133.30
7 purchase totals =	$915.79		$1,009.8036	$1,009.82	$1,009.80	$1,009.90