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	$223.83	13.513%	$254.0761	$254.08	$254.10	$254.10
Purchase #2	$231.89	4.786%	$242.9883	$242.99	$243.00	$243.00
Purchase #3	$81.45	9.663%	$89.3205	$89.32	$89.30	$89.30
Purchase #4	$210.25	6.755%	$224.4524	$224.45	$224.45	$224.50
Purchase #5	$33.84	10.432%	$37.3702	$37.37	$37.35	$37.40
Purchase #6	$65.54	10.783%	$72.6072	$72.61	$72.60	$72.60
Purchase #7	$73.77	6.582%	$78.6255	$78.63	$78.65	$78.60
7 purchase totals =	$920.57		$999.4402	$999.45	$999.45	$999.50