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	$93.93	11.257%	$104.5037	$104.50	$104.50	$104.50
Purchase #2	$64.87	10.542%	$71.7086	$71.71	$71.70	$71.70
Purchase #3	$214.37	12.115%	$240.3409	$240.34	$240.35	$240.30
Purchase #4	$177.26	12.850%	$200.0379	$200.04	$200.05	$200.00
Purchase #5	$75.73	5.115%	$79.6036	$79.60	$79.60	$79.60
Purchase #6	$175.59	5.443%	$185.1474	$185.15	$185.15	$185.10
Purchase #7	$176.52	7.211%	$189.2489	$189.25	$189.25	$189.20
7 purchase totals =	$978.27		$1,070.5910	$1,070.59	$1,070.60	$1,070.40