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	$64.73	11.313%	$72.0529	$72.05	$72.05	$72.10
Purchase #2	$156.72	5.196%	$164.8632	$164.86	$164.85	$164.90
Purchase #3	$175.87	6.637%	$187.5425	$187.54	$187.55	$187.50
Purchase #4	$79.55	11.190%	$88.4516	$88.45	$88.45	$88.50
Purchase #5	$37.98	12.146%	$42.5931	$42.59	$42.60	$42.60
Purchase #6	$140.62	12.563%	$158.2861	$158.29	$158.30	$158.30
Purchase #7	$179.78	4.664%	$188.1649	$188.16	$188.15	$188.20
7 purchase totals =	$835.25		$901.9543	$901.94	$901.95	$902.10