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	$16.83	4.727%	$17.6256	$17.63	$17.65	$17.60
Purchase #2	$152.73	10.519%	$168.7957	$168.80	$168.80	$168.80
Purchase #3	$108.53	10.706%	$120.1492	$120.15	$120.15	$120.10
Purchase #4	$134.63	11.427%	$150.0142	$150.01	$150.00	$150.00
Purchase #5	$236.64	11.180%	$263.0964	$263.10	$263.10	$263.10
Purchase #6	$111.39	10.552%	$123.1439	$123.14	$123.15	$123.10
Purchase #7	$14.43	4.337%	$15.0558	$15.06	$15.05	$15.10
7 purchase totals =	$775.18		$857.8808	$857.89	$857.90	$857.80