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	$245.96	10.728%	$272.3466	$272.35	$272.35	$272.30
Purchase #2	$97.30	12.157%	$109.1288	$109.13	$109.15	$109.10
Purchase #3	$27.59	5.278%	$29.0462	$29.05	$29.05	$29.00
Purchase #4	$28.70	12.646%	$32.3294	$32.33	$32.35	$32.30
Purchase #5	$92.83	13.281%	$105.1588	$105.16	$105.15	$105.20
Purchase #6	$153.48	9.632%	$168.2632	$168.26	$168.25	$168.30
Purchase #7	$154.31	5.511%	$162.814	$162.81	$162.80	$162.80
7 purchase totals =	$800.17		$879.0870	$879.09	$879.10	$879.00