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	$246.31	11.496%	$274.6258	$274.63	$274.65	$274.60
Purchase #2	$153.64	11.119%	$170.7232	$170.72	$170.70	$170.70
Purchase #3	$137.47	7.842%	$148.2504	$148.25	$148.25	$148.30
Purchase #4	$144.56	11.436%	$161.0919	$161.09	$161.10	$161.10
Purchase #5	$72.50	6.791%	$77.4235	$77.42	$77.40	$77.40
Purchase #6	$88.29	3.568%	$91.4402	$91.44	$91.45	$91.40
Purchase #7	$142.69	13.819%	$162.4083	$162.41	$162.40	$162.40
7 purchase totals =	$985.46		$1,085.9633	$1,085.96	$1,085.95	$1,085.90