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	$116.45	12.778%	$131.33	$131.33	$131.35	$131.30
Purchase #2	$39.36	7.246%	$42.212	$42.21	$42.20	$42.20
Purchase #3	$28.91	12.412%	$32.4983	$32.50	$32.50	$32.50
Purchase #4	$165.92	11.806%	$185.5085	$185.51	$185.50	$185.50
Purchase #5	$161.46	3.275%	$166.7478	$166.75	$166.75	$166.70
Purchase #6	$210.67	13.224%	$238.529	$238.53	$238.55	$238.50
Purchase #7	$57.40	10.118%	$63.2077	$63.21	$63.20	$63.20
7 purchase totals =	$780.17		$860.0333	$860.04	$860.05	$859.90