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	$41.77	13.528%	$47.4206	$47.42	$47.40	$47.40
Purchase #2	$114.80	13.512%	$130.3118	$130.31	$130.30	$130.30
Purchase #3	$36.47	3.866%	$37.8799	$37.88	$37.90	$37.90
Purchase #4	$217.45	9.810%	$238.7818	$238.78	$238.80	$238.80
Purchase #5	$248.49	3.420%	$256.9884	$256.99	$257.00	$257.00
Purchase #6	$89.41	6.712%	$95.4112	$95.41	$95.40	$95.40
Purchase #7	$19.59	3.593%	$20.2939	$20.29	$20.30	$20.30
7 purchase totals =	$767.98		$827.0876	$827.08	$827.10	$827.10