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	$5.74	13.253%	$6.5007	$6.50	$6.50	$6.50
Purchase #2	$91.90	8.586%	$99.7905	$99.79	$99.80	$99.80
Purchase #3	$153.95	11.147%	$171.1108	$171.11	$171.10	$171.10
Purchase #4	$89.89	5.144%	$94.5139	$94.51	$94.50	$94.50
Purchase #5	$5.92	10.324%	$6.5312	$6.53	$6.55	$6.50
Purchase #6	$79.97	11.119%	$88.8619	$88.86	$88.85	$88.90
Purchase #7	$207.71	11.513%	$231.6237	$231.62	$231.60	$231.60
7 purchase totals =	$635.08		$698.9327	$698.92	$698.90	$698.90