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	$24.50	13.682%	$27.8521	$27.85	$27.85	$27.90
Purchase #2	$177.77	12.800%	$200.5246	$200.52	$200.50	$200.50
Purchase #3	$212.91	4.322%	$222.112	$222.11	$222.10	$222.10
Purchase #4	$42.59	7.449%	$45.7625	$45.76	$45.75	$45.80
Purchase #5	$246.77	6.659%	$263.2024	$263.20	$263.20	$263.20
Purchase #6	$123.94	11.790%	$138.5525	$138.55	$138.55	$138.60
Purchase #7	$128.58	13.131%	$145.4638	$145.46	$145.45	$145.50
7 purchase totals =	$957.06		$1,043.4699	$1,043.45	$1,043.40	$1,043.60