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	$85.91	5.743%	$90.8438	$90.84	$90.85	$90.80
Purchase #2	$195.46	12.179%	$219.2651	$219.27	$219.25	$219.30
Purchase #3	$118.75	3.664%	$123.101	$123.10	$123.10	$123.10
Purchase #4	$74.33	10.593%	$82.2038	$82.20	$82.20	$82.20
Purchase #5	$115.96	3.421%	$119.927	$119.93	$119.95	$119.90
Purchase #6	$23.84	11.439%	$26.5671	$26.57	$26.55	$26.60
Purchase #7	$50.29	8.242%	$54.4349	$54.43	$54.45	$54.40
7 purchase totals =	$664.54		$716.3427	$716.34	$716.35	$716.30