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	$239.33	13.364%	$271.3141	$271.31	$271.30	$271.30
Purchase #2	$128.88	9.259%	$140.813	$140.81	$140.80	$140.80
Purchase #3	$67.62	7.552%	$72.7267	$72.73	$72.75	$72.70
Purchase #4	$72.30	7.213%	$77.515	$77.52	$77.50	$77.50
Purchase #5	$213.94	13.525%	$242.8754	$242.88	$242.90	$242.90
Purchase #6	$235.86	7.611%	$253.8113	$253.81	$253.80	$253.80
Purchase #7	$68.45	13.197%	$77.4833	$77.48	$77.50	$77.50
7 purchase totals =	$1,026.38		$1,136.5388	$1,136.54	$1,136.55	$1,136.50