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	$20.43	6.139%	$21.6842	$21.68	$21.70	$21.70
Purchase #2	$50.95	8.257%	$55.1569	$55.16	$55.15	$55.20
Purchase #3	$114.59	7.782%	$123.5074	$123.51	$123.50	$123.50
Purchase #4	$25.61	10.344%	$28.2591	$28.26	$28.25	$28.30
Purchase #5	$188.96	10.789%	$209.3469	$209.35	$209.35	$209.30
Purchase #6	$82.28	5.231%	$86.5841	$86.58	$86.60	$86.60
Purchase #7	$225.49	10.555%	$249.2905	$249.29	$249.30	$249.30
7 purchase totals =	$708.31		$773.8291	$773.83	$773.85	$773.90