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	$56.35	13.403%	$63.9026	$63.90	$63.90	$63.90
Purchase #2	$198.90	12.564%	$223.8898	$223.89	$223.90	$223.90
Purchase #3	$71.39	9.334%	$78.0535	$78.05	$78.05	$78.10
Purchase #4	$115.33	5.191%	$121.3168	$121.32	$121.30	$121.30
Purchase #5	$233.85	4.376%	$244.0833	$244.08	$244.10	$244.10
Purchase #6	$29.89	13.615%	$33.9595	$33.96	$33.95	$34.00
Purchase #7	$73.71	11.839%	$82.4365	$82.44	$82.45	$82.40
7 purchase totals =	$779.42		$847.6420	$847.64	$847.65	$847.70