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	$250.61	11.802%	$280.187	$280.19	$280.20	$280.20
Purchase #2	$200.93	6.453%	$213.896	$213.90	$213.90	$213.90
Purchase #3	$238.69	8.467%	$258.8999	$258.90	$258.90	$258.90
Purchase #4	$92.59	7.269%	$99.3204	$99.32	$99.30	$99.30
Purchase #5	$71.41	6.633%	$76.1466	$76.15	$76.15	$76.10
Purchase #6	$106.33	11.741%	$118.8142	$118.81	$118.80	$118.80
Purchase #7	$129.33	3.844%	$134.3014	$134.30	$134.30	$134.30
7 purchase totals =	$1,089.89		$1,181.5655	$1,181.57	$1,181.55	$1,181.50