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	$165.73	13.801%	$188.6024	$188.60	$188.60	$188.60
Purchase #2	$166.48	7.696%	$179.2923	$179.29	$179.30	$179.30
Purchase #3	$230.74	4.644%	$241.4556	$241.46	$241.45	$241.50
Purchase #4	$47.81	10.496%	$52.8281	$52.83	$52.85	$52.80
Purchase #5	$78.76	5.167%	$82.8295	$82.83	$82.85	$82.80
Purchase #6	$190.55	7.374%	$204.6012	$204.60	$204.60	$204.60
Purchase #7	$35.54	8.418%	$38.5318	$38.53	$38.55	$38.50
7 purchase totals =	$915.61		$988.1409	$988.14	$988.20	$988.10