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	$49.39	11.684%	$55.1607	$55.16	$55.15	$55.20
Purchase #2	$174.46	13.712%	$198.382	$198.38	$198.40	$198.40
Purchase #3	$168.97	11.787%	$188.8865	$188.89	$188.90	$188.90
Purchase #4	$239.55	8.764%	$260.5442	$260.54	$260.55	$260.50
Purchase #5	$55.83	3.131%	$57.578	$57.58	$57.60	$57.60
Purchase #6	$54.32	3.125%	$56.0175	$56.02	$56.00	$56.00
Purchase #7	$121.82	3.440%	$126.0106	$126.01	$126.00	$126.00
7 purchase totals =	$864.34		$942.5795	$942.58	$942.60	$942.60