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	$127.46	7.791%	$137.3904	$137.39	$137.40	$137.40
Purchase #2	$156.86	13.754%	$178.4345	$178.43	$178.45	$178.40
Purchase #3	$49.31	12.176%	$55.314	$55.31	$55.30	$55.30
Purchase #4	$241.62	3.688%	$250.5309	$250.53	$250.55	$250.50
Purchase #5	$79.29	12.448%	$89.16	$89.16	$89.15	$89.20
Purchase #6	$31.82	5.665%	$33.6226	$33.62	$33.60	$33.60
Purchase #7	$169.61	13.285%	$192.1427	$192.14	$192.15	$192.10
7 purchase totals =	$855.97		$936.5951	$936.58	$936.60	$936.50