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	$50.30	12.752%	$56.7143	$56.71	$56.70	$56.70
Purchase #2	$198.86	12.362%	$223.4431	$223.44	$223.45	$223.40
Purchase #3	$250.31	12.222%	$280.9029	$280.90	$280.90	$280.90
Purchase #4	$243.78	6.660%	$260.0157	$260.02	$260.00	$260.00
Purchase #5	$166.63	13.716%	$189.485	$189.49	$189.50	$189.50
Purchase #6	$220.81	9.816%	$242.4847	$242.48	$242.50	$242.50
Purchase #7	$190.95	11.829%	$213.5375	$213.54	$213.55	$213.50
7 purchase totals =	$1,321.64		$1,466.5832	$1,466.58	$1,466.60	$1,466.50