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	$18.89	3.751%	$19.5986	$19.60	$19.60	$19.60
Purchase #2	$233.43	3.352%	$241.2546	$241.25	$241.25	$241.30
Purchase #3	$178.93	7.614%	$192.5537	$192.55	$192.55	$192.60
Purchase #4	$225.82	4.653%	$236.3274	$236.33	$236.35	$236.30
Purchase #5	$158.50	12.553%	$178.3965	$178.40	$178.40	$178.40
Purchase #6	$158.35	7.300%	$169.9096	$169.91	$169.90	$169.90
Purchase #7	$127.50	11.234%	$141.8234	$141.82	$141.80	$141.80
7 purchase totals =	$1,101.42		$1,179.8638	$1,179.86	$1,179.85	$1,179.90