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	$167.36	7.311%	$179.5957	$179.60	$179.60	$179.60
Purchase #2	$175.77	5.312%	$185.1069	$185.11	$185.10	$185.10
Purchase #3	$13.78	13.654%	$15.6615	$15.66	$15.65	$15.70
Purchase #4	$21.95	13.169%	$24.8406	$24.84	$24.85	$24.80
Purchase #5	$175.28	9.196%	$191.3987	$191.40	$191.40	$191.40
Purchase #6	$64.74	10.498%	$71.5364	$71.54	$71.55	$71.50
Purchase #7	$165.98	12.735%	$187.1176	$187.12	$187.10	$187.10
7 purchase totals =	$784.86		$855.2574	$855.27	$855.25	$855.20