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	$83.51	7.336%	$89.6363	$89.64	$89.65	$89.60
Purchase #2	$36.93	4.383%	$38.5486	$38.55	$38.55	$38.50
Purchase #3	$165.46	12.411%	$185.9952	$186.00	$186.00	$186.00
Purchase #4	$212.41	3.505%	$219.855	$219.86	$219.85	$219.90
Purchase #5	$37.71	10.466%	$41.6567	$41.66	$41.65	$41.70
Purchase #6	$199.99	10.811%	$221.6109	$221.61	$221.60	$221.60
Purchase #7	$130.87	6.416%	$139.2666	$139.27	$139.25	$139.30
7 purchase totals =	$866.88		$936.5693	$936.59	$936.55	$936.60