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	$40.25	6.632%	$42.9194	$42.92	$42.90	$42.90
Purchase #2	$119.69	13.735%	$136.1294	$136.13	$136.15	$136.10
Purchase #3	$120.47	5.498%	$127.0934	$127.09	$127.10	$127.10
Purchase #4	$75.83	8.817%	$82.5159	$82.52	$82.50	$82.50
Purchase #5	$167.77	11.405%	$186.9042	$186.90	$186.90	$186.90
Purchase #6	$210.82	4.212%	$219.6997	$219.70	$219.70	$219.70
Purchase #7	$190.97	3.166%	$197.0161	$197.02	$197.00	$197.00
7 purchase totals =	$925.80		$992.2781	$992.28	$992.25	$992.20