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	$116.84	6.228%	$124.1168	$124.12	$124.10	$124.10
Purchase #2	$238.35	3.283%	$246.175	$246.18	$246.20	$246.20
Purchase #3	$13.84	13.296%	$15.6802	$15.68	$15.70	$15.70
Purchase #4	$114.96	11.224%	$127.8631	$127.86	$127.85	$127.90
Purchase #5	$67.63	7.628%	$72.7888	$72.79	$72.80	$72.80
Purchase #6	$29.61	10.856%	$32.8245	$32.82	$32.80	$32.80
Purchase #7	$82.48	5.345%	$86.8886	$86.89	$86.90	$86.90
7 purchase totals =	$663.71		$706.3370	$706.34	$706.35	$706.40