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	$78.78	13.115%	$89.112	$89.11	$89.10	$89.10
Purchase #2	$72.37	11.523%	$80.7092	$80.71	$80.70	$80.70
Purchase #3	$172.47	11.842%	$192.8939	$192.89	$192.90	$192.90
Purchase #4	$155.38	7.283%	$166.6963	$166.70	$166.70	$166.70
Purchase #5	$241.37	10.520%	$266.7621	$266.76	$266.75	$266.80
Purchase #6	$210.87	12.488%	$237.2034	$237.20	$237.20	$237.20
Purchase #7	$96.98	13.370%	$109.9462	$109.95	$109.95	$109.90
7 purchase totals =	$1,028.22		$1,143.3231	$1,143.32	$1,143.30	$1,143.30