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	$250.52	12.266%	$281.2488	$281.25	$281.25	$281.20
Purchase #2	$128.40	10.795%	$142.2608	$142.26	$142.25	$142.30
Purchase #3	$213.83	5.719%	$226.0589	$226.06	$226.05	$226.10
Purchase #4	$37.54	11.843%	$41.9859	$41.99	$42.00	$42.00
Purchase #5	$65.78	8.200%	$71.174	$71.17	$71.15	$71.20
Purchase #6	$151.29	12.127%	$169.6369	$169.64	$169.65	$169.60
Purchase #7	$90.64	10.336%	$100.0086	$100.01	$100.00	$100.00
7 purchase totals =	$938.00		$1,032.3739	$1,032.38	$1,032.35	$1,032.40