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	$127.43	7.154%	$136.5463	$136.55	$136.55	$136.50
Purchase #2	$221.50	8.855%	$241.1138	$241.11	$241.10	$241.10
Purchase #3	$83.40	13.153%	$94.3696	$94.37	$94.35	$94.40
Purchase #4	$45.61	10.399%	$50.353	$50.35	$50.35	$50.40
Purchase #5	$187.27	6.760%	$199.9295	$199.93	$199.95	$199.90
Purchase #6	$246.94	13.740%	$280.8696	$280.87	$280.85	$280.90
Purchase #7	$205.97	4.501%	$215.2407	$215.24	$215.25	$215.20
7 purchase totals =	$1,118.12		$1,218.4225	$1,218.42	$1,218.40	$1,218.40