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	$78.50	13.503%	$89.0999	$89.10	$89.10	$89.10
Purchase #2	$57.54	9.222%	$62.8463	$62.85	$62.85	$62.80
Purchase #3	$139.59	4.693%	$146.141	$146.14	$146.15	$146.10
Purchase #4	$220.81	8.858%	$240.3693	$240.37	$240.35	$240.40
Purchase #5	$129.84	12.804%	$146.4647	$146.46	$146.45	$146.50
Purchase #6	$28.56	9.874%	$31.38	$31.38	$31.40	$31.40
Purchase #7	$78.62	5.182%	$82.6941	$82.69	$82.70	$82.70
7 purchase totals =	$733.46		$798.9953	$798.99	$799.00	$799.00