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	$68.77	4.782%	$72.0586	$72.06	$72.05	$72.10
Purchase #2	$123.92	9.457%	$135.6391	$135.64	$135.65	$135.60
Purchase #3	$83.67	3.257%	$86.3951	$86.40	$86.40	$86.40
Purchase #4	$115.96	9.529%	$127.0098	$127.01	$127.00	$127.00
Purchase #5	$96.37	3.243%	$99.4953	$99.50	$99.50	$99.50
Purchase #6	$228.83	5.872%	$242.2669	$242.27	$242.25	$242.30
Purchase #7	$74.53	9.537%	$81.6379	$81.64	$81.65	$81.60
7 purchase totals =	$792.05		$844.5027	$844.52	$844.50	$844.50