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	$82.30	8.837%	$89.5729	$89.57	$89.55	$89.60
Purchase #2	$20.58	9.800%	$22.5968	$22.60	$22.60	$22.60
Purchase #3	$71.82	9.641%	$78.7442	$78.74	$78.75	$78.70
Purchase #4	$170.55	7.384%	$183.1434	$183.14	$183.15	$183.10
Purchase #5	$91.77	5.660%	$96.9642	$96.96	$96.95	$97.00
Purchase #6	$245.65	11.770%	$274.563	$274.56	$274.55	$274.60
Purchase #7	$222.67	9.804%	$244.5006	$244.50	$244.50	$244.50
7 purchase totals =	$905.34		$990.0851	$990.07	$990.05	$990.10