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	$46.63	4.854%	$48.8934	$48.89	$48.90	$48.90
Purchase #2	$39.97	13.179%	$45.2376	$45.24	$45.25	$45.20
Purchase #3	$108.53	11.119%	$120.5975	$120.60	$120.60	$120.60
Purchase #4	$91.49	5.334%	$96.3701	$96.37	$96.35	$96.40
Purchase #5	$118.59	3.274%	$122.4726	$122.47	$122.45	$122.50
Purchase #6	$152.44	10.269%	$168.0941	$168.09	$168.10	$168.10
Purchase #7	$179.87	6.478%	$191.522	$191.52	$191.50	$191.50
7 purchase totals =	$737.52		$793.1873	$793.18	$793.15	$793.20