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	$230.38	4.123%	$239.8786	$239.88	$239.90	$239.90
Purchase #2	$206.97	7.661%	$222.826	$222.83	$222.85	$222.80
Purchase #3	$23.99	10.328%	$26.4677	$26.47	$26.45	$26.50
Purchase #4	$88.26	3.412%	$91.2714	$91.27	$91.25	$91.30
Purchase #5	$181.27	4.548%	$189.5142	$189.51	$189.50	$189.50
Purchase #6	$88.48	3.208%	$91.3184	$91.32	$91.30	$91.30
Purchase #7	$150.59	6.822%	$160.8632	$160.86	$160.85	$160.90
7 purchase totals =	$969.94		$1,022.1395	$1,022.14	$1,022.10	$1,022.20