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	$5.46	11.699%	$6.0988	$6.10	$6.10	$6.10
Purchase #2	$167.63	12.241%	$188.1496	$188.15	$188.15	$188.10
Purchase #3	$34.92	7.651%	$37.5917	$37.59	$37.60	$37.60
Purchase #4	$93.76	4.812%	$98.2717	$98.27	$98.25	$98.30
Purchase #5	$148.45	3.666%	$153.8922	$153.89	$153.90	$153.90
Purchase #6	$13.29	12.350%	$14.9313	$14.93	$14.95	$14.90
Purchase #7	$64.44	12.346%	$72.3958	$72.40	$72.40	$72.40
7 purchase totals =	$527.95		$571.3311	$571.33	$571.35	$571.30