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	$71.89	11.449%	$80.1207	$80.12	$80.10	$80.10
Purchase #2	$139.59	5.630%	$147.4489	$147.45	$147.45	$147.40
Purchase #3	$212.46	8.804%	$231.165	$231.17	$231.15	$231.20
Purchase #4	$241.83	6.200%	$256.8235	$256.82	$256.80	$256.80
Purchase #5	$105.51	7.707%	$113.6417	$113.64	$113.65	$113.60
Purchase #6	$171.48	11.873%	$191.8398	$191.84	$191.85	$191.80
Purchase #7	$65.27	11.200%	$72.5802	$72.58	$72.60	$72.60
7 purchase totals =	$1,008.03		$1,093.6198	$1,093.62	$1,093.60	$1,093.50