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	$161.56	4.177%	$168.3084	$168.31	$168.30	$168.30
Purchase #2	$191.62	11.370%	$213.4072	$213.41	$213.40	$213.40
Purchase #3	$92.43	8.773%	$100.5389	$100.54	$100.55	$100.50
Purchase #4	$136.27	10.768%	$150.9436	$150.94	$150.95	$150.90
Purchase #5	$181.61	10.397%	$200.492	$200.49	$200.50	$200.50
Purchase #6	$205.37	11.524%	$229.0368	$229.04	$229.05	$229.00
Purchase #7	$198.45	11.406%	$221.0852	$221.09	$221.10	$221.10
7 purchase totals =	$1,167.31		$1,283.8121	$1,283.82	$1,283.85	$1,283.70