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	$232.83	10.342%	$256.9093	$256.91	$256.90	$256.90
Purchase #2	$115.74	4.389%	$120.8198	$120.82	$120.80	$120.80
Purchase #3	$53.77	9.443%	$58.8475	$58.85	$58.85	$58.80
Purchase #4	$38.84	12.487%	$43.69	$43.69	$43.70	$43.70
Purchase #5	$59.48	3.809%	$61.7456	$61.75	$61.75	$61.70
Purchase #6	$139.57	8.419%	$151.3204	$151.32	$151.30	$151.30
Purchase #7	$128.48	13.303%	$145.5717	$145.57	$145.55	$145.60
7 purchase totals =	$768.71		$838.9043	$838.91	$838.85	$838.80