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	$98.83	4.400%	$103.1785	$103.18	$103.20	$103.20
Purchase #2	$23.90	6.133%	$25.3658	$25.37	$25.35	$25.40
Purchase #3	$26.66	3.853%	$27.6872	$27.69	$27.70	$27.70
Purchase #4	$165.31	11.822%	$184.8529	$184.85	$184.85	$184.90
Purchase #5	$180.42	11.277%	$200.766	$200.77	$200.75	$200.80
Purchase #6	$151.81	6.823%	$162.168	$162.17	$162.15	$162.20
Purchase #7	$192.40	12.225%	$215.9209	$215.92	$215.90	$215.90
7 purchase totals =	$839.33		$919.9393	$919.95	$919.90	$920.10