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	$79.99	13.328%	$90.6511	$90.65	$90.65	$90.70
Purchase #2	$131.40	6.152%	$139.4837	$139.48	$139.50	$139.50
Purchase #3	$150.35	6.752%	$160.5016	$160.50	$160.50	$160.50
Purchase #4	$237.33	9.240%	$259.2593	$259.26	$259.25	$259.30
Purchase #5	$152.97	6.148%	$162.3746	$162.37	$162.35	$162.40
Purchase #6	$154.53	6.371%	$164.3751	$164.38	$164.40	$164.40
Purchase #7	$137.49	11.334%	$153.0731	$153.07	$153.05	$153.10
7 purchase totals =	$1,044.06		$1,129.7185	$1,129.71	$1,129.70	$1,129.90