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	$249.78	8.198%	$270.257	$270.26	$270.25	$270.30
Purchase #2	$31.78	7.518%	$34.1692	$34.17	$34.15	$34.20
Purchase #3	$81.47	6.571%	$86.8234	$86.82	$86.80	$86.80
Purchase #4	$102.77	8.639%	$111.6483	$111.65	$111.65	$111.60
Purchase #5	$49.88	13.721%	$56.724	$56.72	$56.70	$56.70
Purchase #6	$136.47	7.721%	$147.0068	$147.01	$147.00	$147.00
Purchase #7	$196.41	13.587%	$223.0962	$223.10	$223.10	$223.10
7 purchase totals =	$848.56		$929.7249	$929.73	$929.65	$929.70