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	$119.27	3.215%	$123.1045	$123.10	$123.10	$123.10
Purchase #2	$190.58	8.332%	$206.4591	$206.46	$206.45	$206.50
Purchase #3	$19.33	6.576%	$20.6011	$20.60	$20.60	$20.60
Purchase #4	$177.37	6.147%	$188.2729	$188.27	$188.25	$188.30
Purchase #5	$175.73	7.240%	$188.4529	$188.45	$188.45	$188.50
Purchase #6	$161.42	5.225%	$169.8542	$169.85	$169.85	$169.90
Purchase #7	$89.61	7.745%	$96.5503	$96.55	$96.55	$96.60
7 purchase totals =	$933.31		$993.2950	$993.28	$993.25	$993.50