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	$48.46	12.732%	$54.6299	$54.63	$54.65	$54.60
Purchase #2	$170.94	4.590%	$178.7861	$178.79	$178.80	$178.80
Purchase #3	$225.95	10.771%	$250.2871	$250.29	$250.30	$250.30
Purchase #4	$21.94	4.652%	$22.9606	$22.96	$22.95	$23.00
Purchase #5	$82.96	3.508%	$85.8702	$85.87	$85.85	$85.90
Purchase #6	$96.56	3.322%	$99.7677	$99.77	$99.75	$99.80
Purchase #7	$140.30	10.359%	$154.8337	$154.83	$154.85	$154.80
7 purchase totals =	$787.11		$847.1353	$847.14	$847.15	$847.20