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	$34.45	12.803%	$38.8606	$38.86	$38.85	$38.90
Purchase #2	$111.66	7.280%	$119.7888	$119.79	$119.80	$119.80
Purchase #3	$106.53	11.693%	$118.9866	$118.99	$119.00	$119.00
Purchase #4	$89.95	12.796%	$101.46	$101.46	$101.45	$101.50
Purchase #5	$127.85	3.178%	$131.9131	$131.91	$131.90	$131.90
Purchase #6	$98.59	11.425%	$109.8539	$109.85	$109.85	$109.90
Purchase #7	$51.56	11.627%	$57.5549	$57.55	$57.55	$57.60
7 purchase totals =	$620.59		$678.4179	$678.41	$678.40	$678.60