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	$238.86	4.217%	$248.9327	$248.93	$248.95	$248.90
Purchase #2	$186.30	7.152%	$199.6242	$199.62	$199.60	$199.60
Purchase #3	$151.26	12.347%	$169.9361	$169.94	$169.95	$169.90
Purchase #4	$54.72	11.493%	$61.009	$61.01	$61.00	$61.00
Purchase #5	$90.53	10.872%	$100.3724	$100.37	$100.35	$100.40
Purchase #6	$37.82	9.629%	$41.4617	$41.46	$41.45	$41.50
Purchase #7	$98.44	11.598%	$109.8571	$109.86	$109.85	$109.90
7 purchase totals =	$857.93		$931.1932	$931.19	$931.15	$931.20