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	$129.50	13.720%	$147.2674	$147.27	$147.25	$147.30
Purchase #2	$67.78	6.442%	$72.1464	$72.15	$72.15	$72.10
Purchase #3	$209.88	9.127%	$229.0357	$229.04	$229.05	$229.00
Purchase #4	$179.63	12.377%	$201.8628	$201.86	$201.85	$201.90
Purchase #5	$43.99	10.581%	$48.6446	$48.64	$48.65	$48.60
Purchase #6	$47.46	13.310%	$53.7769	$53.78	$53.80	$53.80
Purchase #7	$85.51	5.586%	$90.2866	$90.29	$90.30	$90.30
7 purchase totals =	$763.75		$843.0204	$843.03	$843.05	$843.00