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	$76.45	7.803%	$82.4154	$82.42	$82.40	$82.40
Purchase #2	$84.89	3.293%	$87.6854	$87.69	$87.70	$87.70
Purchase #3	$165.48	4.785%	$173.3982	$173.40	$173.40	$173.40
Purchase #4	$24.80	13.437%	$28.1324	$28.13	$28.15	$28.10
Purchase #5	$250.56	11.853%	$280.2589	$280.26	$280.25	$280.30
Purchase #6	$46.73	11.514%	$52.1105	$52.11	$52.10	$52.10
Purchase #7	$207.57	7.721%	$223.5965	$223.60	$223.60	$223.60
7 purchase totals =	$856.48		$927.5973	$927.61	$927.60	$927.60