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	$150.90	8.563%	$163.8216	$163.82	$163.80	$163.80
Purchase #2	$229.85	11.669%	$256.6712	$256.67	$256.65	$256.70
Purchase #3	$144.53	10.748%	$160.0641	$160.06	$160.05	$160.10
Purchase #4	$172.71	6.154%	$183.3386	$183.34	$183.35	$183.30
Purchase #5	$175.36	8.720%	$190.6514	$190.65	$190.65	$190.70
Purchase #6	$181.56	10.122%	$199.9375	$199.94	$199.95	$199.90
Purchase #7	$131.59	11.243%	$146.3847	$146.38	$146.40	$146.40
7 purchase totals =	$1,186.50		$1,300.8691	$1,300.86	$1,300.85	$1,300.90