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	$109.54	9.168%	$119.5826	$119.58	$119.60	$119.60
Purchase #2	$152.88	11.223%	$170.0377	$170.04	$170.05	$170.00
Purchase #3	$103.28	6.566%	$110.0614	$110.06	$110.05	$110.10
Purchase #4	$199.68	10.723%	$221.0917	$221.09	$221.10	$221.10
Purchase #5	$179.56	3.519%	$185.8787	$185.88	$185.90	$185.90
Purchase #6	$247.82	10.727%	$274.4037	$274.40	$274.40	$274.40
Purchase #7	$25.88	11.426%	$28.837	$28.84	$28.85	$28.80
7 purchase totals =	$1,018.64		$1,109.8928	$1,109.89	$1,109.95	$1,109.90