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	$90.54	6.304%	$96.2476	$96.25	$96.25	$96.20
Purchase #2	$233.99	8.322%	$253.4626	$253.46	$253.45	$253.50
Purchase #3	$199.78	11.653%	$223.0604	$223.06	$223.05	$223.10
Purchase #4	$216.97	4.836%	$227.4627	$227.46	$227.45	$227.50
Purchase #5	$123.35	3.127%	$127.2072	$127.21	$127.20	$127.20
Purchase #6	$198.93	10.327%	$219.4735	$219.47	$219.45	$219.50
Purchase #7	$175.59	7.395%	$188.5749	$188.57	$188.55	$188.60
7 purchase totals =	$1,239.15		$1,335.4889	$1,335.48	$1,335.40	$1,335.60