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	$28.59	9.524%	$31.3129	$31.31	$31.30	$31.30
Purchase #2	$217.82	9.656%	$238.8527	$238.85	$238.85	$238.90
Purchase #3	$145.34	4.675%	$152.1346	$152.13	$152.15	$152.10
Purchase #4	$132.92	6.683%	$141.803	$141.80	$141.80	$141.80
Purchase #5	$221.96	11.261%	$246.9549	$246.95	$246.95	$247.00
Purchase #6	$153.86	9.506%	$168.4859	$168.49	$168.50	$168.50
Purchase #7	$61.56	8.244%	$66.635	$66.64	$66.65	$66.60
7 purchase totals =	$962.05		$1,046.1790	$1,046.17	$1,046.20	$1,046.20