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	$80.81	11.713%	$90.2753	$90.28	$90.30	$90.30
Purchase #2	$144.50	4.412%	$150.8753	$150.88	$150.90	$150.90
Purchase #3	$112.75	9.541%	$123.5075	$123.51	$123.50	$123.50
Purchase #4	$203.45	3.150%	$209.8587	$209.86	$209.85	$209.90
Purchase #5	$88.26	9.256%	$96.4293	$96.43	$96.45	$96.40
Purchase #6	$200.26	8.506%	$217.2941	$217.29	$217.30	$217.30
Purchase #7	$178.89	13.208%	$202.5178	$202.52	$202.50	$202.50
7 purchase totals =	$1,008.92		$1,090.7580	$1,090.77	$1,090.80	$1,090.80