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	$243.89	13.230%	$276.1566	$276.16	$276.15	$276.20
Purchase #2	$198.33	12.185%	$222.4965	$222.50	$222.50	$222.50
Purchase #3	$71.37	5.553%	$75.3332	$75.33	$75.35	$75.30
Purchase #4	$120.33	13.286%	$136.317	$136.32	$136.30	$136.30
Purchase #5	$168.72	3.258%	$174.2169	$174.22	$174.20	$174.20
Purchase #6	$137.80	13.248%	$156.0557	$156.06	$156.05	$156.10
Purchase #7	$219.41	7.210%	$235.2295	$235.23	$235.25	$235.20
7 purchase totals =	$1,159.85		$1,275.8054	$1,275.82	$1,275.80	$1,275.80