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	$156.57	3.841%	$162.5839	$162.58	$162.60	$162.60
Purchase #2	$35.33	10.533%	$39.0513	$39.05	$39.05	$39.10
Purchase #3	$132.92	6.872%	$142.0543	$142.05	$142.05	$142.10
Purchase #4	$14.37	8.131%	$15.5384	$15.54	$15.55	$15.50
Purchase #5	$78.70	13.300%	$89.1671	$89.17	$89.15	$89.20
Purchase #6	$28.76	6.408%	$30.6029	$30.60	$30.60	$30.60
Purchase #7	$53.72	6.545%	$57.236	$57.24	$57.25	$57.20
7 purchase totals =	$500.37		$536.2339	$536.23	$536.25	$536.30