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	$33.62	11.542%	$37.5004	$37.50	$37.50	$37.50
Purchase #2	$238.62	11.185%	$265.3096	$265.31	$265.30	$265.30
Purchase #3	$194.43	5.815%	$205.7361	$205.74	$205.75	$205.70
Purchase #4	$158.52	6.341%	$168.5718	$168.57	$168.55	$168.60
Purchase #5	$19.98	4.723%	$20.9237	$20.92	$20.90	$20.90
Purchase #6	$42.33	6.697%	$45.1648	$45.16	$45.15	$45.20
Purchase #7	$144.94	8.689%	$157.5338	$157.53	$157.55	$157.50
7 purchase totals =	$832.44		$900.7402	$900.73	$900.70	$900.70