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	$170.98	11.745%	$191.0616	$191.06	$191.05	$191.10
Purchase #2	$106.37	11.499%	$118.6015	$118.60	$118.60	$118.60
Purchase #3	$125.41	10.414%	$138.4702	$138.47	$138.45	$138.50
Purchase #4	$91.55	7.697%	$98.5966	$98.60	$98.60	$98.60
Purchase #5	$231.88	6.246%	$246.3632	$246.36	$246.35	$246.40
Purchase #6	$67.82	6.793%	$72.427	$72.43	$72.45	$72.40
Purchase #7	$162.69	7.196%	$174.3972	$174.40	$174.40	$174.40
7 purchase totals =	$956.70		$1,039.9173	$1,039.92	$1,039.90	$1,040.00