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	$84.84	6.676%	$90.5039	$90.50	$90.50	$90.50
Purchase #2	$28.42	7.501%	$30.5518	$30.55	$30.55	$30.60
Purchase #3	$140.77	4.467%	$147.0582	$147.06	$147.05	$147.10
Purchase #4	$243.85	11.340%	$271.5026	$271.50	$271.50	$271.50
Purchase #5	$138.25	8.531%	$150.0441	$150.04	$150.05	$150.00
Purchase #6	$123.99	3.355%	$128.1499	$128.15	$128.15	$128.10
Purchase #7	$209.30	10.393%	$231.0525	$231.05	$231.05	$231.10
7 purchase totals =	$969.42		$1,048.8630	$1,048.85	$1,048.85	$1,048.90