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	$140.70	3.460%	$145.5682	$145.57	$145.55	$145.60
Purchase #2	$123.32	12.769%	$139.0667	$139.07	$139.05	$139.10
Purchase #3	$204.53	12.351%	$229.7915	$229.79	$229.80	$229.80
Purchase #4	$12.48	7.442%	$13.4088	$13.41	$13.40	$13.40
Purchase #5	$150.72	9.864%	$165.587	$165.59	$165.60	$165.60
Purchase #6	$77.67	6.300%	$82.5632	$82.56	$82.55	$82.60
Purchase #7	$127.76	3.531%	$132.2712	$132.27	$132.25	$132.30
7 purchase totals =	$837.18		$908.2566	$908.26	$908.20	$908.40