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	$167.86	10.158%	$184.9112	$184.91	$184.90	$184.90
Purchase #2	$93.91	12.400%	$105.5548	$105.55	$105.55	$105.60
Purchase #3	$91.71	13.789%	$104.3559	$104.36	$104.35	$104.40
Purchase #4	$52.64	5.638%	$55.6078	$55.61	$55.60	$55.60
Purchase #5	$67.94	3.288%	$70.1739	$70.17	$70.15	$70.20
Purchase #6	$38.54	9.102%	$42.0479	$42.05	$42.05	$42.00
Purchase #7	$35.52	5.336%	$37.4153	$37.42	$37.40	$37.40
7 purchase totals =	$548.12		$600.0668	$600.07	$600.00	$600.10