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	$152.36	10.822%	$168.8484	$168.85	$168.85	$168.80
Purchase #2	$143.53	6.141%	$152.3442	$152.34	$152.35	$152.30
Purchase #3	$79.62	3.164%	$82.1392	$82.14	$82.15	$82.10
Purchase #4	$14.28	6.701%	$15.2369	$15.24	$15.25	$15.20
Purchase #5	$249.31	9.792%	$273.7224	$273.72	$273.70	$273.70
Purchase #6	$71.87	11.335%	$80.0165	$80.02	$80.00	$80.00
Purchase #7	$63.92	5.203%	$67.2458	$67.25	$67.25	$67.20
7 purchase totals =	$774.89		$839.5534	$839.56	$839.55	$839.30