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	$88.32	12.402%	$99.2734	$99.27	$99.25	$99.30
Purchase #2	$41.98	5.631%	$44.3439	$44.34	$44.35	$44.30
Purchase #3	$151.30	13.309%	$171.4365	$171.44	$171.45	$171.40
Purchase #4	$137.49	4.379%	$143.5107	$143.51	$143.50	$143.50
Purchase #5	$126.44	7.611%	$136.0633	$136.06	$136.05	$136.10
Purchase #6	$175.69	7.375%	$188.6471	$188.65	$188.65	$188.60
Purchase #7	$91.45	9.815%	$100.4258	$100.43	$100.45	$100.40
7 purchase totals =	$812.67		$883.7007	$883.70	$883.70	$883.60