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	$215.39	10.722%	$238.4841	$238.48	$238.50	$238.50
Purchase #2	$97.36	12.389%	$109.4219	$109.42	$109.40	$109.40
Purchase #3	$19.71	3.788%	$20.4566	$20.46	$20.45	$20.50
Purchase #4	$94.32	5.300%	$99.319	$99.32	$99.30	$99.30
Purchase #5	$99.30	10.555%	$109.7811	$109.78	$109.80	$109.80
Purchase #6	$199.90	13.104%	$226.0949	$226.09	$226.10	$226.10
Purchase #7	$86.75	3.389%	$89.69	$89.69	$89.70	$89.70
7 purchase totals =	$812.73		$893.2476	$893.24	$893.25	$893.30