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	$131.69	4.157%	$137.1644	$137.16	$137.15	$137.20
Purchase #2	$62.94	7.524%	$67.6756	$67.68	$67.70	$67.70
Purchase #3	$155.56	8.384%	$168.6022	$168.60	$168.60	$168.60
Purchase #4	$70.99	13.219%	$80.3742	$80.37	$80.35	$80.40
Purchase #5	$54.80	10.817%	$60.7277	$60.73	$60.75	$60.70
Purchase #6	$232.59	5.117%	$244.4916	$244.49	$244.50	$244.50
Purchase #7	$214.32	4.274%	$223.48	$223.48	$223.50	$223.50
7 purchase totals =	$922.89		$982.5157	$982.51	$982.55	$982.60