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	$160.93	11.703%	$179.7636	$179.76	$179.75	$179.80
Purchase #2	$39.97	5.243%	$42.0656	$42.07	$42.05	$42.10
Purchase #3	$123.59	7.760%	$133.1806	$133.18	$133.20	$133.20
Purchase #4	$143.58	4.861%	$150.5594	$150.56	$150.55	$150.60
Purchase #5	$75.96	13.625%	$86.3096	$86.31	$86.30	$86.30
Purchase #6	$65.74	9.672%	$72.0984	$72.10	$72.10	$72.10
Purchase #7	$148.58	4.359%	$155.0566	$155.06	$155.05	$155.10
7 purchase totals =	$758.35		$819.0338	$819.04	$819.00	$819.20