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	$99.39	12.739%	$112.0513	$112.05	$112.05	$112.10
Purchase #2	$124.69	13.459%	$141.472	$141.47	$141.45	$141.50
Purchase #3	$55.71	12.527%	$62.6888	$62.69	$62.70	$62.70
Purchase #4	$175.57	7.577%	$188.8729	$188.87	$188.85	$188.90
Purchase #5	$96.65	13.720%	$109.9104	$109.91	$109.90	$109.90
Purchase #6	$206.94	12.103%	$231.9859	$231.99	$232.00	$232.00
Purchase #7	$149.85	13.767%	$170.4798	$170.48	$170.50	$170.50
7 purchase totals =	$908.80		$1,017.4611	$1,017.46	$1,017.45	$1,017.60