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	$82.80	7.863%	$89.3106	$89.31	$89.30	$89.30
Purchase #2	$197.97	7.843%	$213.4968	$213.50	$213.50	$213.50
Purchase #3	$218.56	6.763%	$233.3412	$233.34	$233.35	$233.30
Purchase #4	$76.76	11.428%	$85.5321	$85.53	$85.55	$85.50
Purchase #5	$158.74	8.758%	$172.6424	$172.64	$172.65	$172.60
Purchase #6	$54.68	13.828%	$62.2412	$62.24	$62.25	$62.20
Purchase #7	$131.80	7.545%	$141.7443	$141.74	$141.75	$141.70
7 purchase totals =	$921.31		$998.3086	$998.30	$998.35	$998.10