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	$110.74	11.308%	$123.2625	$123.26	$123.25	$123.30
Purchase #2	$72.75	8.258%	$78.7577	$78.76	$78.75	$78.80
Purchase #3	$94.87	6.206%	$100.7576	$100.76	$100.75	$100.80
Purchase #4	$145.53	4.321%	$151.8184	$151.82	$151.80	$151.80
Purchase #5	$67.64	8.677%	$73.5091	$73.51	$73.50	$73.50
Purchase #6	$45.45	4.484%	$47.488	$47.49	$47.50	$47.50
Purchase #7	$29.80	4.819%	$31.2361	$31.24	$31.25	$31.20
7 purchase totals =	$566.78		$606.8294	$606.84	$606.80	$606.90