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	$151.87	12.686%	$171.1362	$171.14	$171.15	$171.10
Purchase #2	$171.37	13.646%	$194.7552	$194.76	$194.75	$194.80
Purchase #3	$225.90	12.834%	$254.892	$254.89	$254.90	$254.90
Purchase #4	$233.62	9.505%	$255.8256	$255.83	$255.85	$255.80
Purchase #5	$209.43	6.636%	$223.3278	$223.33	$223.35	$223.30
Purchase #6	$42.75	12.464%	$48.0784	$48.08	$48.10	$48.10
Purchase #7	$49.51	12.127%	$55.5141	$55.51	$55.50	$55.50
7 purchase totals =	$1,084.45		$1,203.5293	$1,203.54	$1,203.60	$1,203.50