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	$101.46	7.241%	$108.8067	$108.81	$108.80	$108.80
Purchase #2	$130.72	12.186%	$146.6495	$146.65	$146.65	$146.60
Purchase #3	$88.78	8.369%	$96.21	$96.21	$96.20	$96.20
Purchase #4	$117.92	11.315%	$131.2626	$131.26	$131.25	$131.30
Purchase #5	$37.73	12.742%	$42.5376	$42.54	$42.55	$42.50
Purchase #6	$32.41	3.656%	$33.5949	$33.59	$33.60	$33.60
Purchase #7	$83.73	5.595%	$88.4147	$88.41	$88.40	$88.40
7 purchase totals =	$592.75		$647.4760	$647.47	$647.45	$647.40