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	$103.45	7.451%	$111.1581	$111.16	$111.15	$111.20
Purchase #2	$127.39	10.245%	$140.4411	$140.44	$140.45	$140.40
Purchase #3	$114.96	7.675%	$123.7832	$123.78	$123.80	$123.80
Purchase #4	$28.64	8.331%	$31.026	$31.03	$31.05	$31.00
Purchase #5	$130.87	3.312%	$135.2044	$135.20	$135.20	$135.20
Purchase #6	$67.99	7.228%	$72.9043	$72.90	$72.90	$72.90
Purchase #7	$43.45	3.663%	$45.0416	$45.04	$45.05	$45.00
7 purchase totals =	$616.75		$659.5587	$659.55	$659.60	$659.50