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	$18.32	7.623%	$19.7165	$19.72	$19.70	$19.70
Purchase #2	$18.41	10.366%	$20.3184	$20.32	$20.30	$20.30
Purchase #3	$116.72	8.392%	$126.5151	$126.52	$126.50	$126.50
Purchase #4	$50.74	7.410%	$54.4998	$54.50	$54.50	$54.50
Purchase #5	$221.71	7.459%	$238.2473	$238.25	$238.25	$238.20
Purchase #6	$164.72	10.672%	$182.2989	$182.30	$182.30	$182.30
Purchase #7	$198.83	5.664%	$210.0917	$210.09	$210.10	$210.10
7 purchase totals =	$789.45		$851.6877	$851.70	$851.65	$851.60