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	$166.47	11.221%	$185.1496	$185.15	$185.15	$185.10
Purchase #2	$162.67	11.719%	$181.7333	$181.73	$181.75	$181.70
Purchase #3	$206.85	11.826%	$231.3121	$231.31	$231.30	$231.30
Purchase #4	$216.29	13.306%	$245.0695	$245.07	$245.05	$245.10
Purchase #5	$35.50	12.480%	$39.9304	$39.93	$39.95	$39.90
Purchase #6	$244.96	4.391%	$255.7162	$255.72	$255.70	$255.70
Purchase #7	$47.67	13.305%	$54.0125	$54.01	$54.00	$54.00
7 purchase totals =	$1,080.41		$1,192.9236	$1,192.92	$1,192.90	$1,192.80