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	$97.38	9.210%	$106.3487	$106.35	$106.35	$106.30
Purchase #2	$50.60	5.851%	$53.5606	$53.56	$53.55	$53.60
Purchase #3	$57.47	6.392%	$61.1435	$61.14	$61.15	$61.10
Purchase #4	$166.31	10.422%	$183.6428	$183.64	$183.65	$183.60
Purchase #5	$5.85	9.287%	$6.3933	$6.39	$6.40	$6.40
Purchase #6	$246.36	12.570%	$277.3275	$277.33	$277.35	$277.30
Purchase #7	$87.89	13.337%	$99.6119	$99.61	$99.60	$99.60
7 purchase totals =	$711.86		$788.0283	$788.02	$788.05	$787.90