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	$122.61	7.140%	$131.3644	$131.36	$131.35	$131.40
Purchase #2	$249.83	13.132%	$282.6377	$282.64	$282.65	$282.60
Purchase #3	$65.80	9.752%	$72.2168	$72.22	$72.20	$72.20
Purchase #4	$33.41	11.668%	$37.3083	$37.31	$37.30	$37.30
Purchase #5	$183.37	3.587%	$189.9475	$189.95	$189.95	$189.90
Purchase #6	$6.68	10.654%	$7.3917	$7.39	$7.40	$7.40
Purchase #7	$13.55	7.461%	$14.561	$14.56	$14.55	$14.60
7 purchase totals =	$675.25		$735.4274	$735.43	$735.40	$735.40