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	$127.95	10.323%	$141.1583	$141.16	$141.15	$141.20
Purchase #2	$114.94	4.143%	$119.702	$119.70	$119.70	$119.70
Purchase #3	$203.92	9.161%	$222.6011	$222.60	$222.60	$222.60
Purchase #4	$12.40	7.765%	$13.3629	$13.36	$13.35	$13.40
Purchase #5	$33.35	12.570%	$37.5421	$37.54	$37.55	$37.50
Purchase #6	$31.80	6.760%	$33.9497	$33.95	$33.95	$33.90
Purchase #7	$63.87	6.284%	$67.8836	$67.88	$67.90	$67.90
7 purchase totals =	$588.23		$636.1997	$636.19	$636.20	$636.20