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	$71.48	7.500%	$76.841	$76.84	$76.85	$76.80
Purchase #2	$36.92	5.173%	$38.8299	$38.83	$38.85	$38.80
Purchase #3	$34.42	10.664%	$38.0905	$38.09	$38.10	$38.10
Purchase #4	$104.59	4.324%	$109.1125	$109.11	$109.10	$109.10
Purchase #5	$134.67	13.811%	$153.2693	$153.27	$153.25	$153.30
Purchase #6	$243.37	10.864%	$269.8097	$269.81	$269.80	$269.80
Purchase #7	$145.88	13.550%	$165.6467	$165.65	$165.65	$165.60
7 purchase totals =	$771.33		$851.5996	$851.60	$851.60	$851.50