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	$35.89	12.389%	$40.3364	$40.34	$40.35	$40.30
Purchase #2	$198.77	6.283%	$211.2587	$211.26	$211.25	$211.30
Purchase #3	$189.89	5.615%	$200.5523	$200.55	$200.55	$200.60
Purchase #4	$217.91	8.865%	$237.2277	$237.23	$237.25	$237.20
Purchase #5	$58.89	9.130%	$64.2667	$64.27	$64.25	$64.30
Purchase #6	$103.49	5.322%	$108.9977	$109.00	$109.00	$109.00
Purchase #7	$178.36	10.241%	$196.6258	$196.63	$196.65	$196.60
7 purchase totals =	$983.20		$1,059.2653	$1,059.28	$1,059.30	$1,059.30