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	$18.53	10.678%	$20.5086	$20.51	$20.50	$20.50
Purchase #2	$61.79	12.144%	$69.2938	$69.29	$69.30	$69.30
Purchase #3	$197.86	13.775%	$225.1152	$225.12	$225.10	$225.10
Purchase #4	$37.63	11.686%	$42.0274	$42.03	$42.05	$42.00
Purchase #5	$127.79	9.618%	$140.0808	$140.08	$140.10	$140.10
Purchase #6	$183.71	6.813%	$196.2262	$196.23	$196.25	$196.20
Purchase #7	$33.69	13.176%	$38.129	$38.13	$38.15	$38.10
7 purchase totals =	$661.00		$731.3810	$731.39	$731.45	$731.30