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	$47.57	13.491%	$53.9877	$53.99	$54.00	$54.00
Purchase #2	$183.95	8.682%	$199.9205	$199.92	$199.90	$199.90
Purchase #3	$119.47	4.430%	$124.7625	$124.76	$124.75	$124.80
Purchase #4	$152.56	6.227%	$162.0599	$162.06	$162.05	$162.10
Purchase #5	$127.48	8.694%	$138.5631	$138.56	$138.55	$138.60
Purchase #6	$143.33	6.234%	$152.2652	$152.27	$152.25	$152.30
Purchase #7	$70.51	3.335%	$72.8615	$72.86	$72.85	$72.90
7 purchase totals =	$844.87		$904.4204	$904.42	$904.35	$904.60