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	$15.76	7.120%	$16.8821	$16.88	$16.90	$16.90
Purchase #2	$112.94	4.137%	$117.6123	$117.61	$117.60	$117.60
Purchase #3	$45.89	12.512%	$51.6318	$51.63	$51.65	$51.60
Purchase #4	$105.60	6.340%	$112.295	$112.30	$112.30	$112.30
Purchase #5	$64.33	11.413%	$71.672	$71.67	$71.65	$71.70
Purchase #6	$168.85	7.667%	$181.7957	$181.80	$181.80	$181.80
Purchase #7	$19.42	10.524%	$21.4638	$21.46	$21.45	$21.50
7 purchase totals =	$532.79		$573.3527	$573.35	$573.35	$573.40