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	$249.45	12.552%	$280.761	$280.76	$280.75	$280.80
Purchase #2	$61.46	6.741%	$65.603	$65.60	$65.60	$65.60
Purchase #3	$162.33	4.399%	$169.4709	$169.47	$169.45	$169.50
Purchase #4	$205.45	11.757%	$229.6048	$229.60	$229.60	$229.60
Purchase #5	$232.65	5.358%	$245.1154	$245.12	$245.10	$245.10
Purchase #6	$40.58	5.140%	$42.6658	$42.67	$42.65	$42.70
Purchase #7	$166.90	9.294%	$182.4117	$182.41	$182.40	$182.40
7 purchase totals =	$1,118.82		$1,215.6326	$1,215.63	$1,215.55	$1,215.70