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	$180.85	6.199%	$192.0609	$192.06	$192.05	$192.10
Purchase #2	$104.39	3.548%	$108.0938	$108.09	$108.10	$108.10
Purchase #3	$204.60	9.220%	$223.4641	$223.46	$223.45	$223.50
Purchase #4	$162.29	10.540%	$179.3954	$179.40	$179.40	$179.40
Purchase #5	$148.82	4.753%	$155.8934	$155.89	$155.90	$155.90
Purchase #6	$18.78	5.591%	$19.83	$19.83	$19.85	$19.80
Purchase #7	$41.26	3.290%	$42.6175	$42.62	$42.60	$42.60
7 purchase totals =	$860.99		$921.3551	$921.35	$921.35	$921.40