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	$91.64	10.507%	$101.2686	$101.27	$101.25	$101.30
Purchase #2	$83.51	7.205%	$89.5269	$89.53	$89.55	$89.50
Purchase #3	$126.59	10.473%	$139.8478	$139.85	$139.85	$139.80
Purchase #4	$121.65	10.739%	$134.714	$134.71	$134.70	$134.70
Purchase #5	$24.31	3.129%	$25.0707	$25.07	$25.05	$25.10
Purchase #6	$150.86	8.745%	$164.0527	$164.05	$164.05	$164.10
Purchase #7	$154.47	13.292%	$175.0022	$175.00	$175.00	$175.00
7 purchase totals =	$753.03		$829.4829	$829.48	$829.45	$829.50