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	$140.83	9.629%	$154.3905	$154.39	$154.40	$154.40
Purchase #2	$97.97	12.187%	$109.9096	$109.91	$109.90	$109.90
Purchase #3	$104.89	13.704%	$119.2641	$119.26	$119.25	$119.30
Purchase #4	$79.89	11.801%	$89.3178	$89.32	$89.30	$89.30
Purchase #5	$203.79	9.115%	$222.3655	$222.37	$222.35	$222.40
Purchase #6	$74.52	7.408%	$80.0404	$80.04	$80.05	$80.00
Purchase #7	$113.49	13.232%	$128.507	$128.51	$128.50	$128.50
7 purchase totals =	$815.38		$903.7949	$903.80	$903.75	$903.80