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	$140.44	5.289%	$147.8679	$147.87	$147.85	$147.90
Purchase #2	$104.82	9.417%	$114.6909	$114.69	$114.70	$114.70
Purchase #3	$113.95	9.671%	$124.9701	$124.97	$124.95	$125.00
Purchase #4	$89.97	10.657%	$99.5581	$99.56	$99.55	$99.60
Purchase #5	$35.86	8.269%	$38.8253	$38.83	$38.85	$38.80
Purchase #6	$223.52	7.710%	$240.7534	$240.75	$240.75	$240.80
Purchase #7	$90.89	6.554%	$96.8469	$96.85	$96.85	$96.80
7 purchase totals =	$799.45		$863.5126	$863.52	$863.50	$863.60