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	$139.91	11.693%	$156.2697	$156.27	$156.25	$156.30
Purchase #2	$106.71	11.457%	$118.9358	$118.94	$118.95	$118.90
Purchase #3	$100.27	13.575%	$113.8817	$113.88	$113.90	$113.90
Purchase #4	$123.69	3.215%	$127.6666	$127.67	$127.65	$127.70
Purchase #5	$183.81	8.396%	$199.2427	$199.24	$199.25	$199.20
Purchase #6	$159.94	11.645%	$178.565	$178.57	$178.55	$178.60
Purchase #7	$165.65	5.515%	$174.7856	$174.79	$174.80	$174.80
7 purchase totals =	$979.98		$1,069.3471	$1,069.36	$1,069.35	$1,069.40