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	$37.36	6.563%	$39.8119	$39.81	$39.80	$39.80
Purchase #2	$103.48	12.504%	$116.4191	$116.42	$116.40	$116.40
Purchase #3	$99.83	9.492%	$109.3059	$109.31	$109.30	$109.30
Purchase #4	$233.73	12.760%	$263.5539	$263.55	$263.55	$263.60
Purchase #5	$197.92	6.516%	$210.8165	$210.82	$210.80	$210.80
Purchase #6	$228.95	3.641%	$237.2861	$237.29	$237.30	$237.30
Purchase #7	$80.85	11.209%	$89.9125	$89.91	$89.90	$89.90
7 purchase totals =	$982.12		$1,067.1059	$1,067.11	$1,067.05	$1,067.10