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	$165.40	5.751%	$174.9122	$174.91	$174.90	$174.90
Purchase #2	$65.72	11.749%	$73.4414	$73.44	$73.45	$73.40
Purchase #3	$138.41	3.244%	$142.9	$142.90	$142.90	$142.90
Purchase #4	$173.86	13.798%	$197.8492	$197.85	$197.85	$197.80
Purchase #5	$166.74	3.272%	$172.1957	$172.20	$172.20	$172.20
Purchase #6	$54.55	12.736%	$61.4975	$61.50	$61.50	$61.50
Purchase #7	$37.25	3.498%	$38.553	$38.55	$38.55	$38.60
7 purchase totals =	$801.93		$861.3490	$861.35	$861.35	$861.30