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	$124.42	9.606%	$136.3718	$136.37	$136.35	$136.40
Purchase #2	$76.95	7.462%	$82.692	$82.69	$82.70	$82.70
Purchase #3	$79.41	3.282%	$82.0162	$82.02	$82.00	$82.00
Purchase #4	$79.83	11.375%	$88.9107	$88.91	$88.90	$88.90
Purchase #5	$215.37	4.647%	$225.3782	$225.38	$225.40	$225.40
Purchase #6	$30.67	12.335%	$34.4531	$34.45	$34.45	$34.50
Purchase #7	$102.40	7.179%	$109.7513	$109.75	$109.75	$109.80
7 purchase totals =	$709.05		$759.5733	$759.57	$759.55	$759.70