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	$38.53	12.410%	$43.3116	$43.31	$43.30	$43.30
Purchase #2	$215.58	12.454%	$242.4283	$242.43	$242.45	$242.40
Purchase #3	$42.54	4.689%	$44.5347	$44.53	$44.55	$44.50
Purchase #4	$224.43	11.431%	$250.0846	$250.08	$250.10	$250.10
Purchase #5	$152.37	4.690%	$159.5162	$159.52	$159.50	$159.50
Purchase #6	$35.64	13.587%	$40.4824	$40.48	$40.50	$40.50
Purchase #7	$20.95	8.291%	$22.687	$22.69	$22.70	$22.70
7 purchase totals =	$730.04		$803.0448	$803.04	$803.10	$803.00