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	$27.79	5.516%	$29.3229	$29.32	$29.30	$29.30
Purchase #2	$230.90	10.653%	$255.4978	$255.50	$255.50	$255.50
Purchase #3	$211.98	4.375%	$221.2541	$221.25	$221.25	$221.30
Purchase #4	$38.73	11.760%	$43.2846	$43.28	$43.30	$43.30
Purchase #5	$98.73	6.278%	$104.9283	$104.93	$104.95	$104.90
Purchase #6	$81.36	8.752%	$88.4806	$88.48	$88.50	$88.50
Purchase #7	$179.74	10.474%	$198.566	$198.57	$198.55	$198.60
7 purchase totals =	$869.23		$941.3343	$941.33	$941.35	$941.40