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	$233.48	6.358%	$248.3247	$248.32	$248.30	$248.30
Purchase #2	$125.52	11.292%	$139.6937	$139.69	$139.70	$139.70
Purchase #3	$96.60	9.148%	$105.437	$105.44	$105.45	$105.40
Purchase #4	$160.81	11.532%	$179.3546	$179.35	$179.35	$179.40
Purchase #5	$237.93	11.125%	$264.3997	$264.40	$264.40	$264.40
Purchase #6	$187.77	6.807%	$200.5515	$200.55	$200.55	$200.60
Purchase #7	$126.30	13.120%	$142.8706	$142.87	$142.85	$142.90
7 purchase totals =	$1,168.41		$1,280.6318	$1,280.62	$1,280.60	$1,280.70