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	$180.99	6.841%	$193.3715	$193.37	$193.35	$193.40
Purchase #2	$82.33	8.213%	$89.0918	$89.09	$89.10	$89.10
Purchase #3	$169.45	9.691%	$185.8714	$185.87	$185.85	$185.90
Purchase #4	$249.43	12.579%	$280.8058	$280.81	$280.80	$280.80
Purchase #5	$117.33	12.225%	$131.6736	$131.67	$131.65	$131.70
Purchase #6	$181.40	7.780%	$195.5129	$195.51	$195.50	$195.50
Purchase #7	$131.93	13.698%	$150.0018	$150.00	$150.00	$150.00
7 purchase totals =	$1,112.86		$1,226.3288	$1,226.32	$1,226.25	$1,226.40