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	$115.72	13.814%	$131.7056	$131.71	$131.70	$131.70
Purchase #2	$45.90	9.729%	$50.3656	$50.37	$50.35	$50.40
Purchase #3	$204.90	3.393%	$211.8523	$211.85	$211.85	$211.90
Purchase #4	$128.52	8.445%	$139.3735	$139.37	$139.35	$139.40
Purchase #5	$149.47	12.696%	$168.4467	$168.45	$168.45	$168.40
Purchase #6	$34.44	3.457%	$35.6306	$35.63	$35.65	$35.60
Purchase #7	$236.85	7.775%	$255.2651	$255.27	$255.25	$255.30
7 purchase totals =	$915.80		$992.6394	$992.65	$992.60	$992.70