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	$87.42	3.351%	$90.3494	$90.35	$90.35	$90.30
Purchase #2	$148.63	10.446%	$164.1559	$164.16	$164.15	$164.20
Purchase #3	$19.39	8.626%	$21.0626	$21.06	$21.05	$21.10
Purchase #4	$134.90	5.713%	$142.6068	$142.61	$142.60	$142.60
Purchase #5	$47.27	13.333%	$53.5725	$53.57	$53.55	$53.60
Purchase #6	$209.27	4.566%	$218.8253	$218.83	$218.85	$218.80
Purchase #7	$124.43	12.180%	$139.5856	$139.59	$139.60	$139.60
7 purchase totals =	$771.31		$830.1581	$830.17	$830.15	$830.20