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	$218.45	11.318%	$243.1742	$243.17	$243.15	$243.20
Purchase #2	$228.34	8.374%	$247.4612	$247.46	$247.45	$247.50
Purchase #3	$137.77	4.775%	$144.3485	$144.35	$144.35	$144.30
Purchase #4	$137.82	6.861%	$147.2758	$147.28	$147.30	$147.30
Purchase #5	$81.71	10.736%	$90.4824	$90.48	$90.50	$90.50
Purchase #6	$178.66	8.838%	$194.45	$194.45	$194.45	$194.50
Purchase #7	$205.77	9.656%	$225.6392	$225.64	$225.65	$225.60
7 purchase totals =	$1,188.52		$1,292.8313	$1,292.83	$1,292.85	$1,292.90