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	$19.89	6.199%	$21.123	$21.12	$21.10	$21.10
Purchase #2	$230.82	12.811%	$260.3904	$260.39	$260.40	$260.40
Purchase #3	$250.87	11.304%	$279.2283	$279.23	$279.25	$279.20
Purchase #4	$190.89	6.704%	$203.6873	$203.69	$203.70	$203.70
Purchase #5	$115.63	10.608%	$127.896	$127.90	$127.90	$127.90
Purchase #6	$197.25	6.449%	$209.9707	$209.97	$209.95	$210.00
Purchase #7	$18.99	13.375%	$21.5299	$21.53	$21.55	$21.50
7 purchase totals =	$1,024.34		$1,123.8256	$1,123.83	$1,123.85	$1,123.80