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	$96.74	5.536%	$102.0955	$102.10	$102.10	$102.10
Purchase #2	$118.77	12.116%	$133.1602	$133.16	$133.15	$133.20
Purchase #3	$89.81	11.731%	$100.3456	$100.35	$100.35	$100.30
Purchase #4	$187.64	8.249%	$203.1184	$203.12	$203.10	$203.10
Purchase #5	$184.78	13.848%	$210.3683	$210.37	$210.35	$210.40
Purchase #6	$123.30	6.550%	$131.3762	$131.38	$131.40	$131.40
Purchase #7	$46.73	11.801%	$52.2446	$52.24	$52.25	$52.20
7 purchase totals =	$847.77		$932.7088	$932.72	$932.70	$932.70