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	$211.93	13.387%	$240.3011	$240.30	$240.30	$240.30
Purchase #2	$72.49	8.722%	$78.8126	$78.81	$78.80	$78.80
Purchase #3	$82.43	8.120%	$89.1233	$89.12	$89.10	$89.10
Purchase #4	$217.61	12.654%	$245.1464	$245.15	$245.15	$245.10
Purchase #5	$57.47	6.349%	$61.1188	$61.12	$61.10	$61.10
Purchase #6	$175.51	4.508%	$183.422	$183.42	$183.40	$183.40
Purchase #7	$183.86	4.286%	$191.7402	$191.74	$191.75	$191.70
7 purchase totals =	$1,001.30		$1,089.6644	$1,089.66	$1,089.60	$1,089.50