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	$39.90	5.669%	$42.1619	$42.16	$42.15	$42.20
Purchase #2	$96.84	3.381%	$100.1142	$100.11	$100.10	$100.10
Purchase #3	$177.65	12.609%	$200.0499	$200.05	$200.05	$200.00
Purchase #4	$123.40	12.490%	$138.8127	$138.81	$138.80	$138.80
Purchase #5	$6.61	3.423%	$6.8363	$6.84	$6.85	$6.80
Purchase #6	$205.39	4.740%	$215.1255	$215.13	$215.15	$215.10
Purchase #7	$23.59	8.110%	$25.5031	$25.50	$25.50	$25.50
7 purchase totals =	$673.38		$728.6036	$728.60	$728.60	$728.50