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	$12.67	6.337%	$13.4729	$13.47	$13.45	$13.50
Purchase #2	$37.34	11.385%	$41.5912	$41.59	$41.60	$41.60
Purchase #3	$72.27	13.214%	$81.8198	$81.82	$81.80	$81.80
Purchase #4	$152.43	6.178%	$161.8471	$161.85	$161.85	$161.80
Purchase #5	$234.87	6.816%	$250.8787	$250.88	$250.90	$250.90
Purchase #6	$154.67	13.799%	$176.0129	$176.01	$176.00	$176.00
Purchase #7	$224.69	12.745%	$253.3267	$253.33	$253.35	$253.30
7 purchase totals =	$888.94		$978.9493	$978.95	$978.95	$978.90