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	$22.91	8.190%	$24.7863	$24.79	$24.80	$24.80
Purchase #2	$94.53	10.673%	$104.6192	$104.62	$104.60	$104.60
Purchase #3	$225.82	12.827%	$254.7859	$254.79	$254.80	$254.80
Purchase #4	$118.27	7.843%	$127.5459	$127.55	$127.55	$127.50
Purchase #5	$198.28	10.435%	$218.9705	$218.97	$218.95	$219.00
Purchase #6	$129.55	9.529%	$141.8948	$141.89	$141.90	$141.90
Purchase #7	$182.62	5.604%	$192.854	$192.85	$192.85	$192.90
7 purchase totals =	$971.98		$1,065.4566	$1,065.46	$1,065.45	$1,065.50