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	$99.90	10.721%	$110.6103	$110.61	$110.60	$110.60
Purchase #2	$35.65	7.507%	$38.3262	$38.33	$38.35	$38.30
Purchase #3	$96.45	10.418%	$106.4982	$106.50	$106.50	$106.50
Purchase #4	$69.59	12.745%	$78.4592	$78.46	$78.45	$78.50
Purchase #5	$142.80	9.717%	$156.6759	$156.68	$156.70	$156.70
Purchase #6	$213.62	8.819%	$232.4591	$232.46	$232.45	$232.50
Purchase #7	$248.96	12.779%	$280.7746	$280.77	$280.75	$280.80
7 purchase totals =	$906.97		$1,003.8035	$1,003.81	$1,003.80	$1,003.90