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	$80.34	11.740%	$89.7719	$89.77	$89.75	$89.80
Purchase #2	$38.94	5.318%	$41.0108	$41.01	$41.00	$41.00
Purchase #3	$233.37	13.249%	$264.2892	$264.29	$264.30	$264.30
Purchase #4	$143.61	4.263%	$149.7321	$149.73	$149.75	$149.70
Purchase #5	$135.94	7.141%	$145.6475	$145.65	$145.65	$145.60
Purchase #6	$128.30	8.351%	$139.0143	$139.01	$139.00	$139.00
Purchase #7	$43.61	11.240%	$48.5118	$48.51	$48.50	$48.50
7 purchase totals =	$804.11		$877.9776	$877.97	$877.95	$877.90