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	$37.33	7.390%	$40.0887	$40.09	$40.10	$40.10
Purchase #2	$94.35	13.425%	$107.0165	$107.02	$107.00	$107.00
Purchase #3	$233.61	11.453%	$260.3654	$260.37	$260.35	$260.40
Purchase #4	$250.53	10.803%	$277.5948	$277.59	$277.60	$277.60
Purchase #5	$199.45	11.614%	$222.6141	$222.61	$222.60	$222.60
Purchase #6	$91.41	11.809%	$102.2046	$102.20	$102.20	$102.20
Purchase #7	$84.83	5.417%	$89.4252	$89.43	$89.45	$89.40
7 purchase totals =	$991.51		$1,099.3093	$1,099.31	$1,099.30	$1,099.30