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	$173.70	6.254%	$184.5632	$184.56	$184.55	$184.60
Purchase #2	$105.48	5.741%	$111.5356	$111.54	$111.55	$111.50
Purchase #3	$249.49	11.467%	$278.099	$278.10	$278.10	$278.10
Purchase #4	$146.56	9.248%	$160.1139	$160.11	$160.10	$160.10
Purchase #5	$222.49	6.190%	$236.2621	$236.26	$236.25	$236.30
Purchase #6	$103.36	11.828%	$115.5854	$115.59	$115.60	$115.60
Purchase #7	$79.82	5.110%	$83.8988	$83.90	$83.90	$83.90
7 purchase totals =	$1,080.90		$1,170.0580	$1,170.06	$1,170.05	$1,170.10