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	$26.67	5.176%	$28.0504	$28.05	$28.05	$28.10
Purchase #2	$183.35	9.270%	$200.3465	$200.35	$200.35	$200.30
Purchase #3	$139.92	11.121%	$155.4805	$155.48	$155.50	$155.50
Purchase #4	$115.71	9.863%	$127.1225	$127.12	$127.10	$127.10
Purchase #5	$226.81	12.788%	$255.8145	$255.81	$255.80	$255.80
Purchase #6	$228.29	9.391%	$249.7287	$249.73	$249.75	$249.70
Purchase #7	$72.38	11.700%	$80.8485	$80.85	$80.85	$80.80
7 purchase totals =	$993.13		$1,097.3916	$1,097.39	$1,097.40	$1,097.30