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	$85.32	7.800%	$91.975	$91.98	$92.00	$92.00
Purchase #2	$123.90	8.508%	$134.4414	$134.44	$134.45	$134.40
Purchase #3	$57.57	11.380%	$64.1215	$64.12	$64.10	$64.10
Purchase #4	$27.61	9.194%	$30.1485	$30.15	$30.15	$30.10
Purchase #5	$150.66	10.712%	$166.7987	$166.80	$166.80	$166.80
Purchase #6	$116.67	9.657%	$127.9368	$127.94	$127.95	$127.90
Purchase #7	$109.94	12.266%	$123.4252	$123.43	$123.45	$123.40
7 purchase totals =	$671.67		$738.8471	$738.86	$738.90	$738.70