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	$55.79	3.280%	$57.6199	$57.62	$57.60	$57.60
Purchase #2	$47.50	11.426%	$52.9274	$52.93	$52.95	$52.90
Purchase #3	$130.56	8.130%	$141.1745	$141.17	$141.15	$141.20
Purchase #4	$105.88	6.396%	$112.6521	$112.65	$112.65	$112.70
Purchase #5	$117.74	11.645%	$131.4508	$131.45	$131.45	$131.50
Purchase #6	$182.52	7.663%	$196.5065	$196.51	$196.50	$196.50
Purchase #7	$118.77	13.837%	$135.2042	$135.20	$135.20	$135.20
7 purchase totals =	$758.76		$827.5354	$827.53	$827.50	$827.60