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	$221.97	9.854%	$243.8429	$243.84	$243.85	$243.80
Purchase #2	$249.25	10.633%	$275.7528	$275.75	$275.75	$275.80
Purchase #3	$241.96	5.442%	$255.1275	$255.13	$255.15	$255.10
Purchase #4	$30.69	9.640%	$33.6485	$33.65	$33.65	$33.60
Purchase #5	$36.60	3.757%	$37.9751	$37.98	$38.00	$38.00
Purchase #6	$129.52	10.117%	$142.6235	$142.62	$142.60	$142.60
Purchase #7	$81.52	4.775%	$85.4126	$85.41	$85.40	$85.40
7 purchase totals =	$991.51		$1,074.3829	$1,074.38	$1,074.40	$1,074.30