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	$16.90	6.851%	$18.0578	$18.06	$18.05	$18.10
Purchase #2	$118.62	10.571%	$131.1593	$131.16	$131.15	$131.20
Purchase #3	$143.52	4.620%	$150.1506	$150.15	$150.15	$150.20
Purchase #4	$76.76	7.806%	$82.7519	$82.75	$82.75	$82.80
Purchase #5	$224.39	7.782%	$241.852	$241.85	$241.85	$241.90
Purchase #6	$135.89	7.489%	$146.0668	$146.07	$146.05	$146.10
Purchase #7	$238.43	12.304%	$267.7664	$267.77	$267.75	$267.80
7 purchase totals =	$954.51		$1,037.8048	$1,037.81	$1,037.75	$1,038.10