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	$20.55	6.565%	$21.8991	$21.90	$21.90	$21.90
Purchase #2	$149.62	10.148%	$164.8034	$164.80	$164.80	$164.80
Purchase #3	$172.62	4.207%	$179.8821	$179.88	$179.90	$179.90
Purchase #4	$152.54	6.537%	$162.5115	$162.51	$162.50	$162.50
Purchase #5	$74.76	10.476%	$82.5919	$82.59	$82.60	$82.60
Purchase #6	$150.99	4.417%	$157.6592	$157.66	$157.65	$157.70
Purchase #7	$133.98	5.169%	$140.9054	$140.91	$140.90	$140.90
7 purchase totals =	$855.06		$910.2526	$910.25	$910.25	$910.30