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	$102.84	3.626%	$106.569	$106.57	$106.55	$106.60
Purchase #2	$145.28	11.795%	$162.4158	$162.42	$162.40	$162.40
Purchase #3	$96.61	10.443%	$106.699	$106.70	$106.70	$106.70
Purchase #4	$231.42	7.381%	$248.5011	$248.50	$248.50	$248.50
Purchase #5	$65.63	9.439%	$71.8248	$71.82	$71.80	$71.80
Purchase #6	$148.66	6.301%	$158.0271	$158.03	$158.05	$158.00
Purchase #7	$70.42	10.564%	$77.8592	$77.86	$77.85	$77.90
7 purchase totals =	$860.86		$931.8960	$931.90	$931.85	$931.90