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	$240.85	7.364%	$258.5862	$258.59	$258.60	$258.60
Purchase #2	$79.93	8.444%	$86.6793	$86.68	$86.70	$86.70
Purchase #3	$120.94	13.510%	$137.279	$137.28	$137.30	$137.30
Purchase #4	$86.90	4.673%	$90.9608	$90.96	$90.95	$91.00
Purchase #5	$103.31	11.768%	$115.4675	$115.47	$115.45	$115.50
Purchase #6	$79.32	11.729%	$88.6234	$88.62	$88.60	$88.60
Purchase #7	$152.43	4.680%	$159.5637	$159.56	$159.55	$159.60
7 purchase totals =	$863.68		$937.1599	$937.16	$937.15	$937.30