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	$250.72	11.772%	$280.2348	$280.23	$280.25	$280.20
Purchase #2	$204.50	13.575%	$232.2609	$232.26	$232.25	$232.30
Purchase #3	$235.81	4.249%	$245.8296	$245.83	$245.85	$245.80
Purchase #4	$205.72	13.774%	$234.0559	$234.06	$234.05	$234.10
Purchase #5	$29.55	5.612%	$31.2083	$31.21	$31.20	$31.20
Purchase #6	$56.72	4.620%	$59.3405	$59.34	$59.35	$59.30
Purchase #7	$145.69	11.724%	$162.7707	$162.77	$162.75	$162.80
7 purchase totals =	$1,128.71		$1,245.7007	$1,245.70	$1,245.70	$1,245.70