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	$167.90	10.244%	$185.0997	$185.10	$185.10	$185.10
Purchase #2	$88.35	6.715%	$94.2827	$94.28	$94.30	$94.30
Purchase #3	$117.96	4.736%	$123.5466	$123.55	$123.55	$123.50
Purchase #4	$102.59	8.651%	$111.4651	$111.47	$111.45	$111.50
Purchase #5	$173.30	9.850%	$190.3701	$190.37	$190.35	$190.40
Purchase #6	$73.64	9.403%	$80.5644	$80.56	$80.55	$80.60
Purchase #7	$108.47	6.447%	$115.4631	$115.46	$115.45	$115.50
7 purchase totals =	$832.21		$900.7917	$900.79	$900.75	$900.90