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	$184.25	8.776%	$200.4198	$200.42	$200.40	$200.40
Purchase #2	$116.86	12.333%	$131.2723	$131.27	$131.25	$131.30
Purchase #3	$113.31	13.815%	$128.9638	$128.96	$128.95	$129.00
Purchase #4	$131.43	7.180%	$140.8667	$140.87	$140.85	$140.90
Purchase #5	$97.29	6.631%	$103.7413	$103.74	$103.75	$103.70
Purchase #6	$89.64	13.691%	$101.9126	$101.91	$101.90	$101.90
Purchase #7	$56.44	11.167%	$62.7427	$62.74	$62.75	$62.70
7 purchase totals =	$789.22		$869.9192	$869.91	$869.85	$869.90