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	$97.38	12.276%	$109.3344	$109.33	$109.35	$109.30
Purchase #2	$209.57	4.252%	$218.4809	$218.48	$218.50	$218.50
Purchase #3	$95.45	6.359%	$101.5197	$101.52	$101.50	$101.50
Purchase #4	$64.47	11.198%	$71.6894	$71.69	$71.70	$71.70
Purchase #5	$26.84	12.704%	$30.2498	$30.25	$30.25	$30.20
Purchase #6	$123.67	3.642%	$128.1741	$128.17	$128.15	$128.20
Purchase #7	$158.38	6.798%	$169.1467	$169.15	$169.15	$169.10
7 purchase totals =	$775.76		$828.5950	$828.59	$828.60	$828.50