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	$82.73	6.760%	$88.3225	$88.32	$88.30	$88.30
Purchase #2	$20.46	3.755%	$21.2283	$21.23	$21.25	$21.20
Purchase #3	$99.76	6.712%	$106.4559	$106.46	$106.45	$106.50
Purchase #4	$96.85	10.476%	$106.996	$107.00	$107.00	$107.00
Purchase #5	$99.75	13.664%	$113.3798	$113.38	$113.40	$113.40
Purchase #6	$33.33	11.538%	$37.1756	$37.18	$37.20	$37.20
Purchase #7	$102.49	6.409%	$109.0586	$109.06	$109.05	$109.10
7 purchase totals =	$535.37		$582.6167	$582.63	$582.65	$582.70