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	$78.79	4.200%	$82.0992	$82.10	$82.10	$82.10
Purchase #2	$146.55	12.473%	$164.8292	$164.83	$164.85	$164.80
Purchase #3	$51.40	12.512%	$57.8312	$57.83	$57.85	$57.80
Purchase #4	$30.91	5.825%	$32.7105	$32.71	$32.70	$32.70
Purchase #5	$84.38	12.302%	$94.7604	$94.76	$94.75	$94.80
Purchase #6	$145.29	8.314%	$157.3694	$157.37	$157.35	$157.40
Purchase #7	$96.46	6.590%	$102.8167	$102.82	$102.80	$102.80
7 purchase totals =	$633.78		$692.4166	$692.42	$692.40	$692.40