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	$104.50	6.260%	$111.0417	$111.04	$111.05	$111.00
Purchase #2	$20.94	13.485%	$23.7638	$23.76	$23.75	$23.80
Purchase #3	$191.84	4.274%	$200.0392	$200.04	$200.05	$200.00
Purchase #4	$201.94	3.610%	$209.23	$209.23	$209.25	$209.20
Purchase #5	$76.30	8.353%	$82.6733	$82.67	$82.65	$82.70
Purchase #6	$145.64	4.731%	$152.5302	$152.53	$152.55	$152.50
Purchase #7	$194.30	3.728%	$201.5435	$201.54	$201.55	$201.50
7 purchase totals =	$935.46		$980.8217	$980.81	$980.85	$980.70