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	$166.35	13.502%	$188.8106	$188.81	$188.80	$188.80
Purchase #2	$187.62	13.404%	$212.7686	$212.77	$212.75	$212.80
Purchase #3	$201.37	8.117%	$217.7152	$217.72	$217.70	$217.70
Purchase #4	$38.54	10.318%	$42.5166	$42.52	$42.50	$42.50
Purchase #5	$106.35	13.664%	$120.8817	$120.88	$120.90	$120.90
Purchase #6	$165.98	11.730%	$185.4495	$185.45	$185.45	$185.40
Purchase #7	$246.46	7.845%	$265.7948	$265.79	$265.80	$265.80
7 purchase totals =	$1,112.67		$1,233.9370	$1,233.94	$1,233.90	$1,233.90