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	$250.52	12.145%	$280.9457	$280.95	$280.95	$280.90
Purchase #2	$31.31	12.117%	$35.1038	$35.10	$35.10	$35.10
Purchase #3	$190.47	12.703%	$214.6654	$214.67	$214.65	$214.70
Purchase #4	$80.65	12.112%	$90.4183	$90.42	$90.40	$90.40
Purchase #5	$216.68	3.519%	$224.305	$224.31	$224.30	$224.30
Purchase #6	$151.69	8.809%	$165.0524	$165.05	$165.05	$165.10
Purchase #7	$44.78	9.229%	$48.9127	$48.91	$48.90	$48.90
7 purchase totals =	$966.10		$1,059.4033	$1,059.41	$1,059.35	$1,059.40