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	$153.85	5.635%	$162.5194	$162.52	$162.50	$162.50
Purchase #2	$106.70	11.757%	$119.2447	$119.24	$119.25	$119.20
Purchase #3	$228.72	12.427%	$257.143	$257.14	$257.15	$257.10
Purchase #4	$42.96	6.420%	$45.718	$45.72	$45.70	$45.70
Purchase #5	$102.47	11.697%	$114.4559	$114.46	$114.45	$114.50
Purchase #6	$167.70	10.319%	$185.005	$185.01	$185.00	$185.00
Purchase #7	$77.84	10.618%	$86.1051	$86.11	$86.10	$86.10
7 purchase totals =	$880.24		$970.1911	$970.20	$970.15	$970.10