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	$241.86	9.480%	$264.7883	$264.79	$264.80	$264.80
Purchase #2	$120.94	10.684%	$133.8612	$133.86	$133.85	$133.90
Purchase #3	$33.27	12.849%	$37.5449	$37.54	$37.55	$37.50
Purchase #4	$55.90	6.289%	$59.4156	$59.42	$59.40	$59.40
Purchase #5	$96.54	4.500%	$100.8843	$100.88	$100.90	$100.90
Purchase #6	$148.68	6.477%	$158.31	$158.31	$158.30	$158.30
Purchase #7	$81.86	6.162%	$86.9042	$86.90	$86.90	$86.90
7 purchase totals =	$779.05		$841.7085	$841.70	$841.70	$841.70