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	$51.71	4.437%	$54.0044	$54.00	$54.00	$54.00
Purchase #2	$107.27	11.223%	$119.3089	$119.31	$119.30	$119.30
Purchase #3	$95.72	5.268%	$100.7625	$100.76	$100.75	$100.80
Purchase #4	$39.52	3.353%	$40.8451	$40.85	$40.85	$40.80
Purchase #5	$189.61	11.594%	$211.5934	$211.59	$211.60	$211.60
Purchase #6	$120.74	11.863%	$135.0634	$135.06	$135.05	$135.10
Purchase #7	$240.80	12.221%	$270.2282	$270.23	$270.25	$270.20
7 purchase totals =	$845.37		$931.8059	$931.80	$931.80	$931.80