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	$18.78	12.756%	$21.1756	$21.18	$21.20	$21.20
Purchase #2	$95.58	5.175%	$100.5263	$100.53	$100.55	$100.50
Purchase #3	$237.46	5.230%	$249.8792	$249.88	$249.90	$249.90
Purchase #4	$90.85	6.154%	$96.4409	$96.44	$96.45	$96.40
Purchase #5	$221.93	8.743%	$241.3333	$241.33	$241.35	$241.30
Purchase #6	$39.46	9.335%	$43.1436	$43.14	$43.15	$43.10
Purchase #7	$149.99	10.163%	$165.2335	$165.23	$165.25	$165.20
7 purchase totals =	$854.05		$917.7324	$917.73	$917.85	$917.60