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	$100.32	10.668%	$111.0221	$111.02	$111.00	$111.00
Purchase #2	$205.82	13.507%	$233.6201	$233.62	$233.60	$233.60
Purchase #3	$139.87	8.281%	$151.4526	$151.45	$151.45	$151.50
Purchase #4	$215.53	11.507%	$240.331	$240.33	$240.35	$240.30
Purchase #5	$98.77	3.505%	$102.2319	$102.23	$102.25	$102.20
Purchase #6	$37.48	7.254%	$40.1988	$40.20	$40.20	$40.20
Purchase #7	$176.85	13.471%	$200.6735	$200.67	$200.65	$200.70
7 purchase totals =	$974.64		$1,079.5300	$1,079.52	$1,079.50	$1,079.50