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	$74.31	4.805%	$77.8806	$77.88	$77.90	$77.90
Purchase #2	$152.89	6.163%	$162.3126	$162.31	$162.30	$162.30
Purchase #3	$162.98	9.776%	$178.9129	$178.91	$178.90	$178.90
Purchase #4	$38.36	8.525%	$41.6302	$41.63	$41.65	$41.60
Purchase #5	$67.56	5.598%	$71.342	$71.34	$71.35	$71.30
Purchase #6	$159.29	3.551%	$164.9464	$164.95	$164.95	$164.90
Purchase #7	$73.55	10.852%	$81.5316	$81.53	$81.55	$81.50
7 purchase totals =	$728.94		$778.5563	$778.55	$778.60	$778.40