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	$42.88	12.164%	$48.0959	$48.10	$48.10	$48.10
Purchase #2	$148.65	3.141%	$153.3191	$153.32	$153.30	$153.30
Purchase #3	$250.38	4.370%	$261.3216	$261.32	$261.30	$261.30
Purchase #4	$144.27	12.769%	$162.6918	$162.69	$162.70	$162.70
Purchase #5	$34.35	7.752%	$37.0128	$37.01	$37.00	$37.00
Purchase #6	$151.77	9.360%	$165.9757	$165.98	$166.00	$166.00
Purchase #7	$27.56	3.133%	$28.4235	$28.42	$28.40	$28.40
7 purchase totals =	$799.86		$856.8404	$856.84	$856.80	$856.80