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	$51.73	10.788%	$57.3106	$57.31	$57.30	$57.30
Purchase #2	$123.59	4.227%	$128.8141	$128.81	$128.80	$128.80
Purchase #3	$60.74	4.681%	$63.5832	$63.58	$63.60	$63.60
Purchase #4	$58.55	6.579%	$62.402	$62.40	$62.40	$62.40
Purchase #5	$102.84	13.127%	$116.3398	$116.34	$116.35	$116.30
Purchase #6	$105.55	3.601%	$109.3509	$109.35	$109.35	$109.40
Purchase #7	$64.76	12.291%	$72.7197	$72.72	$72.70	$72.70
7 purchase totals =	$567.76		$610.5203	$610.51	$610.50	$610.50