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	$79.41	12.542%	$89.3696	$89.37	$89.35	$89.40
Purchase #2	$76.30	4.320%	$79.5962	$79.60	$79.60	$79.60
Purchase #3	$149.94	4.465%	$156.6348	$156.63	$156.65	$156.60
Purchase #4	$165.48	6.322%	$175.9416	$175.94	$175.95	$175.90
Purchase #5	$75.86	8.423%	$82.2497	$82.25	$82.25	$82.20
Purchase #6	$179.47	9.448%	$196.4263	$196.43	$196.45	$196.40
Purchase #7	$82.83	13.419%	$93.945	$93.95	$93.95	$93.90
7 purchase totals =	$809.29		$874.1632	$874.17	$874.20	$874.00