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	$209.95	10.492%	$231.978	$231.98	$232.00	$232.00
Purchase #2	$148.98	10.715%	$164.9432	$164.94	$164.95	$164.90
Purchase #3	$153.32	11.729%	$171.3029	$171.30	$171.30	$171.30
Purchase #4	$58.37	5.367%	$61.5027	$61.50	$61.50	$61.50
Purchase #5	$48.33	11.671%	$53.9706	$53.97	$53.95	$54.00
Purchase #6	$97.86	6.752%	$104.4675	$104.47	$104.45	$104.50
Purchase #7	$18.76	10.757%	$20.778	$20.78	$20.80	$20.80
7 purchase totals =	$735.57		$808.9429	$808.94	$808.95	$809.00