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	$91.55	13.689%	$104.0823	$104.08	$104.10	$104.10
Purchase #2	$89.52	3.185%	$92.3712	$92.37	$92.35	$92.40
Purchase #3	$56.97	13.608%	$64.7225	$64.72	$64.70	$64.70
Purchase #4	$70.97	4.813%	$74.3858	$74.39	$74.40	$74.40
Purchase #5	$84.39	5.763%	$89.2534	$89.25	$89.25	$89.30
Purchase #6	$33.96	9.801%	$37.2884	$37.29	$37.30	$37.30
Purchase #7	$6.97	13.577%	$7.9163	$7.92	$7.90	$7.90
7 purchase totals =	$434.33		$470.0199	$470.02	$470.00	$470.10