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	$166.38	6.280%	$176.8287	$176.83	$176.85	$176.80
Purchase #2	$33.64	6.578%	$35.8528	$35.85	$35.85	$35.90
Purchase #3	$96.67	7.395%	$103.8187	$103.82	$103.80	$103.80
Purchase #4	$145.41	6.843%	$155.3604	$155.36	$155.35	$155.40
Purchase #5	$82.92	12.415%	$93.2145	$93.21	$93.20	$93.20
Purchase #6	$53.84	13.414%	$61.0621	$61.06	$61.05	$61.10
Purchase #7	$56.49	5.110%	$59.3766	$59.38	$59.40	$59.40
7 purchase totals =	$635.35		$685.5138	$685.51	$685.50	$685.60