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	$225.48	5.763%	$238.4744	$238.47	$238.45	$238.50
Purchase #2	$178.82	9.689%	$196.1459	$196.15	$196.15	$196.10
Purchase #3	$96.78	12.666%	$109.0382	$109.04	$109.05	$109.00
Purchase #4	$60.43	11.615%	$67.4489	$67.45	$67.45	$67.40
Purchase #5	$52.76	12.806%	$59.5164	$59.52	$59.50	$59.50
Purchase #6	$48.33	3.135%	$49.8451	$49.85	$49.85	$49.80
Purchase #7	$71.53	12.165%	$80.2316	$80.23	$80.25	$80.20
7 purchase totals =	$734.13		$800.7005	$800.71	$800.70	$800.50