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	$99.70	9.756%	$109.4267	$109.43	$109.45	$109.40
Purchase #2	$225.56	3.613%	$233.7095	$233.71	$233.70	$233.70
Purchase #3	$90.98	11.714%	$101.6374	$101.64	$101.65	$101.60
Purchase #4	$25.73	9.612%	$28.2032	$28.20	$28.20	$28.20
Purchase #5	$143.79	7.196%	$154.1371	$154.14	$154.15	$154.10
Purchase #6	$197.32	9.384%	$215.8365	$215.84	$215.85	$215.80
Purchase #7	$159.55	6.204%	$169.4485	$169.45	$169.45	$169.40
7 purchase totals =	$942.63		$1,012.3989	$1,012.41	$1,012.45	$1,012.20